AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON JANUARY 21, 2005
                                                           REGISTRATION NO. 333-
================================================================================
                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                    FORM S-3
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                          LEXICON GENETICS INCORPORATED
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

           DELAWARE                                          76-0474169
 (STATE OR OTHER JURISDICTION OF                           (I.R.S. EMPLOYER
 INCORPORATION OR ORGANIZATION)                         IDENTIFICATION NUMBER)

                                  ------------

                          8800 TECHNOLOGY FOREST PLACE
                         THE WOODLANDS, TEXAS 77381-1160
                                 (281) 863-3000
 (ADDRESS, INCLUDING ZIP CODE, AND TELEPHONE NUMBER, INCLUDING AREA CODE, OF
                    REGISTRANT'S PRINCIPAL EXECUTIVE OFFICES)

                                  ------------

                          ARTHUR T. SANDS, M.D., PH.D.
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                          8800 TECHNOLOGY FOREST PLACE
                        THE WOODLANDS, TEXAS 77381-1160
                                 (281) 863-3000
 (NAME, ADDRESS, INCLUDING ZIP CODE, AND TELEPHONE NUMBER, INCLUDING AREA CODE,
                             OF AGENT FOR SERVICE)

                                  ------------

                                   COPIES TO:
      DAVID P. OELMAN                              JEFFREY L. WADE
  VINSON & ELKINS L.L.P.          EXECUTIVE VICE PRESIDENT AND GENERAL COUNSEL
   2300 FIRST CITY TOWER                    LEXICON GENETICS INCORPORATED
        1001 FANNIN                          8800 TECHNOLOGY FOREST PLACE
 HOUSTON, TEXAS 77002-6760                 THE WOODLANDS, TEXAS 77381-1160
      (713) 758-3708                               (281) 863-3000

        APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC:
                                        
          From time to time after this registration statement becomes
           effective, subject to market conditions and other factors.

      If the only securities being registered on this Form are being offered
pursuant to dividend or interest reinvestment plans, check the following box.[ ]

      If any of the securities being registered on this Form are to be offered
on a delayed or continuous basis pursuant to Rule 415 under the Securities Act
of 1933, other than securities offered only in connection with dividend or
interest reinvestment plans, check the following box. [X]

      If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list the Securities Act registration statement number of the earlier
effective registration statement for the same offering.[ ]

      If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. [ ]

      If delivery of the Prospectus is expected to be made pursuant to Rule 434,
please check the following box. [ ]

                               CALCULATION OF REGISTRATION FEE



                                                                PROPOSED MAXIMUM          PROPOSED MAXIMUM
     TITLE OF EACH CLASS OF        AMOUNT TO BE REGISTERED     AGGREGATE OFFERING            AGGREGATE                AMOUNT OF
   SECURITIES TO BE REGISTERED             (1) (2)             PRICE PER UNIT (2)        OFFERING PRICE (2)        REGISTRATION FEE
---------------------------------  -----------------------    --------------------      --------------------       ----------------
                                                                                                       
Common Stock, par value $0.001                                                                                          N/A
Preferred Stock, par value $0.01                                                                                        N/A
Debt Securities                                                                                                         N/A
Warrants                                                                                                                N/A
Units                                                                                                                   N/A
                                      -----------------                                    ---------------         -------------
     Total                            $     150,000,000                                    $   150,000,000         $   17,655 (3)
                                      -----------------                                    ---------------         -------------


(1)   There are being registered hereunder such indeterminate (i) number of
      shares of common stock and preferred stock, (ii) principal amount of debt
      securities, (iii) number of warrants to purchase common stock, preferred
      stock or debt securities and (iv) number of units as shall have an
      aggregate initial offering price not to exceed $150,000,000. If any debt
      securities are issued at an original issued discount, then the offering
      price of such debt securities shall be in such greater principal amount as
      shall result in an aggregate initial offering price not to exceed
      $150,000,000, less the aggregate dollar amount of all securities
      previously issued hereunder. Any securities registered hereunder may be
      sold separately or as units with other securities registered hereunder.
      The proposed maximum initial offering price per security or unit will be
      determined, from time to time, by the registrant in connection with the
      issuance by the registrant of the securities registered hereunder. The
      securities registered also include such indeterminate numbers of shares of
      common stock and preferred stock and amount of debt securities as may be
      issued upon conversion of or exchange for preferred stock or debt
      securities that provide for conversion or exchange, upon exercise of
      warrants or pursuant to the antidilution provisions of any such
      securities.

(2)   The amount to be registered, proposed maximum aggregate offering price per
      unit and proposed maximum aggregate offering price are not specified as to
      each class of security pursuant to General Instruction II.D. of Form S-3
      under the Securities Act.

(3)   Calculated pursuant to Rule 457(o) under the Securities Act. Of this
      amount, $644 was previously paid with respect to 1,760,000 unsold shares
      of Common Stock registered on Form S-3 (Registration No. 333-101549) filed
      by the registrant on November 27, 2002. Accordingly, pursuant to Rule
      457(p) under the Securities Act, the fee being paid herewith is $17,011.

      THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION
STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(a) OF
THE SECURITIES ACT OF 1933, AS AMENDED, OR UNTIL THE REGISTRATION STATEMENT
SHALL BECOME EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID
SECTION 8(a), MAY DETERMINE.
================================================================================


The information in this prospectus is not complete and may be changed.  We may
not sell these securities until the registration statement filed with the
Securities and Exchange Commission is effective. This prospectus is not an offer
to sell these securities and it is not soliciting an offer to buy these
securities in any state where the offer or sale is not permitted.

                  SUBJECT TO COMPLETION, DATED JANUARY 21, 2005


                                  $150,000,000

                                 [LEXICON LOGO]

                          LEXICON GENETICS INCORPORATED

                                  COMMON STOCK
                                 PREFERRED STOCK
                                 DEBT SECURITIES
                                    WARRANTS
                                      UNITS

      We may offer common stock, preferred stock, debt securities and/or
warrants, either individually or in units, from time to time in one or more
offerings in amounts, at prices and on terms to be determined in light of market
conditions at the time of sale. We may also offer common stock or preferred
stock upon conversion of debt securities, common stock upon conversion of
preferred stock or common stock, preferred stock or debt securities upon the
exercise of warrants.

      Each time we sell these securities, we will provide a supplement to this
prospectus that contains specific information about the offering. The supplement
may also add, update or change information contained in this prospectus. You
should carefully read this prospectus and any supplement before you invest.

      Our common stock is listed on The Nasdaq National Market under the symbol
"LEXG". The prospectus supplement will contain information, where applicable,
regarding any other listing on The Nasdaq National Market or any securities
exchange of the securities covered by the prospectus supplement. The last
reported sale price of our common stock on January 19, 2005 was $7.25 per share.

      INVESTING IN OUR SECURITIES INVOLVES RISKS. SEE "RISK FACTORS" ON PAGE 4.

      Neither the Securities and Exchange Commission nor any state securities
commission has approved or disapproved of these securities or determined if this
prospectus is truthful or complete. Any representation to the contrary is a
criminal offense.

                  The date of this prospectus is      , 2005.



                                TABLE OF CONTENTS



                                                    PAGE
                                                    ----
                                                 
Lexicon Genetics Incorporated................         3       
Risk Factors.................................         4       
Description of Capital Stock.................         4       
Description of Debt Securities...............         6       
Description of Warrants......................        12       
Description of Units.........................        14       
Legal Ownership of Securities................        15       
Special Note Regarding Forward Looking
   Statements................................        17
Ratio of Earnings to Fixed Charges...........        18
Use of Proceeds..............................        18
Plan of Distribution.........................        18
Legal Matters................................        20
Experts......................................        20
Where You Can Find More Information..........        20
Documents Incorporated by Reference..........        20



                          LEXICON GENETICS INCORPORATED

      Lexicon Genetics is a biopharmaceutical company focused on the discovery
of breakthrough treatments for human disease. We are systematically discovering
the physiological and behavioral functions of genes to identify those that
encode potential targets for therapeutic intervention, or drug targets. We make
our discoveries using our proprietary technology to knock out, or disrupt, the
function of genes in mice to model the effects on physiology that could be
expected from prospective drugs directed against those targets. For targets that
we believe have high pharmaceutical value, we engage in programs for the
discovery and development of potential small molecule, antibody and protein
drugs. We focus our discovery efforts in six therapeutic areas - diabetes and
obesity, cardiovascular disease, psychiatric and neurological disorders, cancer,
immune system disorders and ophthalmic disease - and we have advanced targets
into drug discovery programs in each of these areas with potential for
addressing large medical markets.

      We make our discoveries using proprietary technology to knock out genes in
mice, analyze the resulting effects on physiology and behavior, and identify
those genes that exhibit a favorable therapeutic profile in mouse models. Using
this information, we select potential targets encoded by the corresponding human
genes for our drug discovery programs. Our physiology-based approach to
understanding gene function and our use of mouse models in our drug discovery
efforts allow us to make highly-informed decisions throughout the drug discovery
and development process, which we believe will increase our likelihood of
success in discovering breakthrough therapeutics.

      The scope of our gene knockout technology, combined with the size and
sophistication of our facilities and our evaluative technologies, provides us
with what we believe to be a significant competitive advantage. We are using
these technologies in our Genome5000 program to discover the physiological and
behavioral functions of 5,000 genes from the human genome that belong to gene
families that we consider to be pharmaceutically important. We have completed
our analysis of more than 40% of these genes, and we expect to complete the
analysis of the remaining genes by the end of 2008. To date, we have advanced
into drug discovery programs more than 60 targets, each of which we have
validated in living mammals, or in vivo. As of the date of this prospectus, none
of our programs had yet advanced into clinical development.

      We are working both independently and through strategic collaborations and
alliances to commercialize our technology and turn our discoveries into drugs.
We have established multiple collaborations with leading pharmaceutical and
biotechnology companies, as well as research institutes and academic
institutions. We are working with Bristol-Myers Squibb Company to discover and
develop novel small molecule drugs in the neuroscience field. We are working
with Genentech, Inc. to discover the functions of secreted proteins and
potential antibody targets identified through Genentech's internal drug
discovery research. We are working with Takeda Pharmaceutical Company Limited
for the discovery of new drugs for the treatment of high blood pressure. In
addition, we have established collaborations and license agreements with many
other leading pharmaceutical and biotechnology companies under which we receive
fees and, in some cases, are eligible to receive milestone and royalty payments,
in return for granting access to some of our technologies and discoveries for
use in such companies' own drug discovery efforts.

      Lexicon Genetics was incorporated in Delaware in July 1995, and commenced
operations in September 1995. Our corporate headquarters are located at 8800
Technology Forest Place, The Woodlands, Texas 77381, and our telephone number is
(281) 863-3000.

      Our annual report on Form 10-K, quarterly reports on Form 10-Q, current
reports on Form 8-K, and amendments to those reports filed or furnished pursuant
to Section 13(a) or 15(d) of the Securities Exchange Act of 1934 are made
available free of charge on our corporate website located at
www.lexicon-genetics.com as soon as reasonably practicable after the filing of
those reports with the Securities and Exchange Commission. Information found on
our website should not be considered part of this prospectus.

                                       3



                                  RISK FACTORS

      You should carefully consider the risk factors and all other information
contained in this prospectus and any prospectus supplement and incorporated
herein by reference before purchasing our securities. Investing in our
securities involves a high degree of risk.

      For a discussion of these risks, please see:

      -     Our most recent annual report on Form 10-K, and

      -     Our other filings with the Securities and Exchange Commission that
            are incorporated by reference into this prospectus.

      For more information about our SEC filings, please see "Where You Can Find
More Information" and "Documents Incorporated By Reference" on page 20 of this
prospectus. See also "Special Note Regarding Forward-Looking Statements" on page
17 of this prospectus.

                          DESCRIPTION OF CAPITAL STOCK

      Our authorized capital stock consists of 120 million shares of common
stock, $0.001 par value, and five million shares of preferred stock, $0.01 par
value. As of December 31, 2004, there were 63,491,237 shares of our common stock
outstanding and no shares of preferred stock outstanding.

      The following summary description of our capital stock is based on the
provisions of our restated certificate of incorporation, restated bylaws and the
applicable provisions of the Delaware General Corporation Law. This information
may not be complete in all respects and is qualified entirely by reference to
the provisions of our restated certificate of incorporation, restated bylaws and
the Delaware General Corporation Law. For information on how to obtain copies of
our restated certificate of incorporation and restated bylaws, see "Where You
Can Find More Information" on page 20 of this prospectus.

COMMON STOCK

      The holders of common stock are entitled to one vote for each share held
of record on all matters submitted to a vote of the stockholders and do not have
cumulative voting rights. Accordingly, holders of a majority of the shares of
common stock entitled to vote in any election of directors may elect all of the
directors standing for election. Subject to preferences that may be applicable
to any outstanding shares of preferred stock, the holders of common stock are
entitled to receive ratably such dividends as may be declared by the board of
directors out of funds legally available therefor. Upon the liquidation,
dissolution or winding up of Lexicon, holders of our common stock are entitled
to share ratably in all assets remaining after payment of liabilities and the
liquidation preferences of any outstanding shares of preferred stock. Holders of
common stock have no preemptive rights and no right to convert their common
stock into any other securities. There are no redemption or sinking fund
provisions applicable to our common stock. All outstanding shares of our common
stock are, and all shares of common stock that may be issued under this
prospectus will be, fully paid and non-assessable.

PREFERRED STOCK

      Pursuant to our restated certificate of incorporation, our board of
directors has the authority, without further action by the stockholders, to
issue up to five million shares of preferred stock, in one or more series. Our
board of directors is authorized to fix or alter from time to time the
designation, powers, preferences and rights of the shares of each series of
preferred stock, including dividend rights, conversion rights, voting rights,
terms of redemption, liquidation preferences and sinking fund terms. Our board
of directors may also establish from time to time the number of shares
constituting any series of preferred stock, and to increase or decrease the
number of shares of any series subsequent to the issuance of shares of that
series, but not below the number of shares of any series then outstanding.

      We will fix the rights, preferences, privileges and restrictions of the
preferred stock of each series in the certificate of designation relating to
that series. We will incorporate by reference as an exhibit to the registration
statement that includes this prospectus or as an exhibit to a report filed under
the Securities Exchange Act of 1934, the form of any certificate of designation
that describes the terms of the series of preferred stock we are offering before
the issuance of the related series of preferred stock. This description will
include:

                                       4



      -     the title and stated value;

      -     the number of shares we are offering;

      -     the liquidation preference per share;

      -     the purchase price;

      -     the dividend rate, period and payment date and method of calculation
            for dividends;

      -     whether dividends will be cumulative or non-cumulative and, if
            cumulative, the date from which dividends will accumulate;

      -     the provisions for a sinking fund, if any;

      -     the provisions for redemption or repurchase, if applicable, and any
            restrictions on our ability to exercise those redemption and
            repurchase rights;

      -     whether the preferred stock will be convertible into our common
            stock, and, if applicable, the conversion price, or how it will be
            calculated, and the conversion period;

      -     whether the preferred stock will be exchangeable into debt
            securities, and, if applicable, the exchange price, or how it will
            be calculated, and the exchange period;

      -     voting rights, if any, of the preferred stock;

      -     preemption rights, if any;

      -     restrictions on transfer, sale or other assignment, if any;

      -     the relative ranking and preferences of the preferred stock as to
            dividend rights and rights if we liquidate, dissolve or wind up our
            affairs;

      -     any limitations on issuance of any class or series of preferred
            stock ranking senior to or on a parity with the series of preferred
            stock as to dividend rights and rights if we liquidate, dissolve or
            wind up our affairs; and

      -     any other specific terms, preferences, rights or limitations of, or
            restrictions on, the preferred stock.

      If we issue shares of preferred stock under this prospectus, the shares
will be fully paid and non-assessable and will not have, or be subject to, any
preemptive or similar rights.

      The Delaware General Corporation Law of the State of Delaware provides
that the holders of preferred stock will have the right to vote separately as a
class on any proposal involving fundamental changes in the rights of holders of
that preferred stock. This right is in addition to any voting rights that may be
provided for in the applicable certificate of designation.

      The issuance of preferred stock could adversely affect the voting power,
conversion or other rights of holders of common stock. Preferred stock could be
issued quickly with terms designed to delay or prevent a change in control of
our company or make removal of management more difficult. Additionally, the
issuance of preferred stock may have the effect of decreasing the market price
of our common stock.

REGISTRATION RIGHTS

      As of the date of this prospectus, certain holders of our common stock are
entitled to rights with respect to the registration of those shares of common
stock under the Securities Act of 1933. These rights are described in the
Amended and Restated Registration Rights Agreement dated as of May 7, 1998 by
and among Lexicon and the stockholders named therein. These registration rights
require, among other things, that if we propose to register any of our
securities under the Securities Act, either for our own account or for the
account of others, the holders of these shares are entitled to notice of the
registration and are entitled to include, at our expense, their shares of common
stock in the registration and any related underwriting, provided, among other
conditions, that the underwriters may limit the number of shares to be included
in the registration and in some cases exclude these shares entirely. In
addition, the holders of these shares may require us, at our expense and subject
to certain limitations, to file a registration statement under the Securities
Act with respect to their shares of our common stock.

                                      5



These holders have waived these registration rights with respect to any
offerings of our securities pursuant to this prospectus.

ANTI-TAKEOVER EFFECTS OF PROVISIONS OF DELAWARE LAW AND OUR CHARTER DOCUMENTS

      Delaware Takeover Statute. We are subject to the provisions of Section 203
of the Delaware General Corporation Law. In general, the statute prohibits a
publicly-held Delaware corporation such as Lexicon from engaging in a business
combination with an interested stockholder for a period of three years after the
date of the transaction in which the person became an interested stockholder,
unless the business combination is approved in a prescribed manner. For purposes
of Section 203, a business combination includes a merger, asset sale or other
transaction resulting in a financial benefit to the interested stockholder. An
interested stockholder is a person who, together with affiliates and associates,
owns (or within three years prior, did own) 15% or more of our voting stock.

      Charter Documents. Our restated certificate of incorporation requires that
any action required or permitted to be taken by our stockholders must be
effected at a duly called annual or special meeting of stockholders and may not
be effected by a consent in writing. Additionally, our restated certificate of
incorporation:

      -     does not provide for the use of cumulative voting in the election of
            directors;

      -     provides for a board of directors, classified into three classes of
            directors;

      -     provides that the authorized number of directors may be changed only
            by resolution of our board of directors; and

      -     provides for the authority of our board of directors to issue up to
            five million shares of "blank check" preferred stock and to
            determine the price, powers, preferences and rights of these shares,
            without stockholder approval.

      Our restated bylaws provide that candidates for director may be nominated
only by our board of directors or by a stockholder who gives written notice to
us not less than 120 days nor more than 150 days in advance of the first
anniversary of the date of our proxy statement relating to the previous year's
annual meeting of stockholders. The authorized number of directors is fixed in
accordance with our restated certificate of incorporation. Our board of
directors currently consists of eight members, divided into three classes. As a
result, a portion of the board of directors will be elected each year. The board
of directors may appoint new directors to fill vacancies or newly created
directorships. Our restated bylaws also limit who may call a special meeting of
stockholders.

      Delaware law and these charter provisions may have the effect of deterring
hostile takeovers or delaying changes in control of our management, which could
depress the market price of our common stock.

TRANSFER AGENT AND REGISTRAR

      The transfer agent and registrar for our common stock is Mellon Investor
Services L.L.C. The transfer agent for any series of preferred stock will be
named and described in the prospectus supplement for that series.

                         DESCRIPTION OF DEBT SECURITIES

      The following description, together with the additional information we may
include in any applicable prospectus supplements, summarizes the material terms
and provisions of the debt securities that we may offer under this prospectus
and the related indenture. While the terms summarized below will apply generally
to any debt securities we may offer under this prospectus, we will describe the
particular terms of any debt securities that we may offer in more detail in the
applicable prospectus supplement. If we indicate in the prospectus supplement,
the terms of any debt securities offered under that prospectus supplement may
differ from the terms described below. However, no prospectus supplement shall
fundamentally change the terms that are set forth in this prospectus or offer a
security that is not registered and described in this prospectus at the time of
its effectiveness.

      We may offer debt securities in the form of either senior debt securities
or subordinated debt securities. Unless otherwise specified in a supplement to
this prospectus, the debt securities will be our direct, unsecured obligations
and will rank equally with all of our other unsecured and unsubordinated
indebtedness.

      The debt securities will be issued under an indenture between us and a
trustee. The following summary of the general features of the debt securities to
be governed by the indenture is subject to, and qualified in its entirety by
reference to, the provisions of the indenture applicable to a particular series
of debt securities. We have filed a form

                                       6



of indenture as an exhibit to the registration statement which includes this
prospectus. Capitalized terms used in the summary have the meanings specified in
the indenture.

GENERAL

      The terms of each series of debt securities will be established by or
pursuant to a resolution of our board of directors, or a committee thereof, and
set forth or determined in the manner provided in an officer's certificate or by
a supplemental indenture. The particular terms of each series of debt securities
will be described in a prospectus supplement relating to such series, including
any pricing supplement.

      We can issue an unlimited amount of debt securities under the indenture
that may be in one or more series with the same or various maturities, at par,
at a premium or at a discount. We will set forth in a prospectus supplement,
including any pricing supplement, relating to any series of debt securities
being offered, the aggregate principal amount and the following terms of the
debt securities:

      -     the title of the debt securities;

      -     the price or prices (expressed as a percentage of the principal
            amount) at which we will sell the debt securities;

      -     any limit on the aggregate principal amount of the debt securities;

      -     the date or dates on which we will pay the principal on the debt
            securities;

      -     the rate or rates (which may be fixed or variable) per annum or the
            method used to determine the rate or rates (including any commodity,
            commodity index, stock exchange index or financial index) at which
            the debt securities will bear interest, the date or dates from which
            interest will accrue, the date or dates on which interest will
            commence and be payable and any regular record date for the interest
            payable on any interest payment date;

      -     the place or places where principal of, and premium and interest on,
            the debt securities will be payable;

      -     the terms and conditions upon which we may redeem the debt
            securities;

      -     any obligation we have to redeem or purchase the debt securities
            pursuant to any sinking fund or analogous provisions or at the
            option of a holder of debt securities;

      -     the dates on which and the price or prices at which we will
            repurchase debt securities at the option of the holders of debt
            securities and other detailed terms and provisions of these
            repurchase obligations;

      -     the denominations in which the debt securities will be issued, if
            other than denominations of $1,000 and any integral multiple
            thereof;

      -     whether the debt securities will be issued in the form of
            certificated debt securities or global debt securities;

      -     the portion of principal amount of the debt securities payable upon
            declaration of acceleration of the maturity date, if other than the
            principal amount;

      -     the currency of denomination of the debt securities;

      -     the designation of the currency, currencies or currency units in
            which payment of principal of, and premium and interest on, the debt
            securities will be made;

      -     if payments of principal of, or premium or interest on, the debt
            securities will be made in one or more currencies or currency units
            other than that or those in which the debt securities are
            denominated, the manner in which the exchange rate with respect to
            these payments will be determined;

      -     the manner in which the amounts of payment of principal of, or
            premium or interest on, the debt securities will be determined, if
            these amounts may be determined by reference to an index based on a
            currency or currencies other than that in which the debt securities
            are denominated or designated to be payable or by reference to a
            commodity, commodity index, stock exchange index or financial index;

      -     any provisions relating to any security provided for the debt
            securities;

                                       7



      -     any addition to or change in the events of default described in this
            prospectus or in the indenture with respect to the debt securities
            and any change in the acceleration provisions described in this
            prospectus or in the indenture with respect to the debt securities;

      -     any addition to or change in the covenants described in this
            prospectus or in the indenture with respect to the debt securities;

      -     any conversion provisions, including the conversion price, the
            conversion period, provisions as to whether conversion will be
            mandatory, at the option of the holder or at our option, the events
            requiring an adjustment of the conversion price and provisions
            affecting conversion if such series of debt securities are redeemed;

      -     whether the debt securities will be senior debt securities or
            subordinated debt securities and, if applicable, a description of
            the subordination terms thereof;

      -     any depositaries, interest rate calculation agents, exchange rate
            calculation agents or other agents with respect to the debt
            securities; and

      -     any other terms of the debt securities, which may modify, delete,
            supplement or add to any provision of the indenture as it applies to
            that series.

      We may issue debt securities that provide for an amount less than their
stated principal amount to be due and payable upon declaration of acceleration
of their maturity pursuant to the terms of the indenture. We will provide you
with information on the federal income tax considerations and other special
considerations applicable to any of these debt securities in the applicable
prospectus supplement.

      If we denominate the purchase price of any of the debt securities in a
foreign currency or currencies or a foreign currency unit or units, or if the
principal of, and premium and interest on, any series of debt securities is
payable in a foreign currency or currencies or a foreign currency unit or units,
we will provide you with information on the restrictions, elections, general tax
considerations, specific terms and other information with respect to that issue
of debt securities and such foreign currency or currencies or foreign currency
unit or units in the applicable prospectus supplement.

TRANSFER AND EXCHANGE

      Each debt security will be represented by either one or more global
securities registered in the name of The Depository Trust Company, as
Depositary, or a nominee (we will refer to any debt security represented by a
global debt security as a "book-entry debt security"), or a certificate issued
in definitive registered form (we will refer to any debt security represented by
a certificated security as a "certificated debt security") as set forth in the
applicable prospectus supplement. Except as set forth under the heading "Legal
Ownership of Securities" below, book-entry securities will not be issuable in
certificated form.

      You may transfer or exchange certificated debt securities at any office we
maintain for this purpose in accordance with the terms of the indenture. No
service charge will be made for any transfer or exchange of certificated debt
securities, but we may require payment of a sum sufficient to cover any tax or
other governmental charge payable in connection with a transfer or exchange.

      You may effect the transfer of certificated debt securities and the right
to receive the principal of, and any premium and interest on, certificated debt
securities only by surrendering the certificate representing those certificated
debt securities and either reissuance by us or the trustee of the certificate to
the new holder or the issuance by us or the trustee of a new certificate to the
new holder.

NO PROTECTION IN THE EVENT OF A CHANGE OF CONTROL

      Unless we state otherwise in the applicable prospectus supplement, the
debt securities will not contain any provisions which may afford holders of the
debt securities protection in the event we have a change in control or in the
event of a highly leveraged transaction (whether or not such transaction results
in a change in control) which could adversely affect holders of debt securities.

                                       8


COVENANTS

      We will set forth in the applicable prospectus supplement any restrictive
covenants applicable to any issue of debt securities.

CONSOLIDATION, MERGER AND SALE OF ASSETS

      We may not consolidate with or merge with or into, or convey, transfer or
lease all or substantially all of our properties and assets to, any person,
which we refer to as a successor person, unless:

      -     we are the surviving corporation or the successor person (if other
            than Lexicon) is organized and validly existing under the laws of
            any U.S. domestic jurisdiction and expressly assumes our obligations
            on the debt securities and under the indenture;

      -     immediately after giving effect to the transaction, no event of
            default, and no event which, after notice or lapse of time, or both,
            would become an event of default, shall have occurred and be
            continuing under the indenture; and

      -     certain other conditions are met.

EVENTS OF DEFAULT

      Event of default means, with respect to any series of debt securities, any
of the following:

      -     default in the payment of any interest upon any debt security of
            that series when it becomes due and payable, and continuance of that
            default for a period of 30 days (unless the entire amount of the
            payment is deposited by us with the trustee or with a paying agent
            prior to the expiration of the 30-day period);

      -     default in the payment of principal of or premium on any debt
            security of that series when due and payable;

      -     default in the deposit of any sinking fund payment, when and as due
            in respect of any debt security of that series;

      -     default in the performance or breach of any other covenant or
            warranty by us in the indenture (other than a covenant or warranty
            that has been included in the indenture solely for the benefit of a
            series of debt securities other than that series), which default
            continues uncured for a period of 90 days after we receive written
            notice from the trustee or we and the trustee receive written notice
            from the holders of not less than a majority in principal amount of
            the outstanding debt securities of that series as provided in the
            indenture;

      -     certain events of bankruptcy, insolvency or reorganization of our
            company; and

      -     any other event of default provided with respect to debt securities
            of that series that is described in the applicable prospectus
            supplement accompanying this prospectus.

      No event of default with respect to a particular series of debt securities
(except as to certain events of bankruptcy, insolvency or reorganization)
necessarily constitutes an event of default with respect to any other series of
debt securities. The occurrence of an event of default may constitute an event
of default under our bank credit agreements in existence from time to time. In
addition, the occurrence of certain events of default or an acceleration under
the indenture may constitute an event of default under certain of our other
indebtedness outstanding from time to time.

      If an event of default with respect to debt securities of any series at
the time outstanding occurs and is continuing, then the trustee or the holders
of not less than a majority in principal amount of the outstanding debt
securities of that series may, by a notice in writing to us (and to the trustee
if given by the holders), declare to be due and payable immediately the
principal (or, if the debt securities of that series are discount securities,
that portion of the principal amount as may be specified in the terms of that
series) of, and accrued and unpaid interest, if any, on all debt securities of
that series. In the case of an event of default resulting from certain events of
bankruptcy, insolvency or reorganization, the principal (or such specified
amount) of and accrued and unpaid interest, if any, on all outstanding debt
securities will become and be immediately due and payable without any
declaration or other act on the part of the trustee or any holder of outstanding
debt securities. At any time after a declaration of acceleration with respect to
debt securities of any series has been made, but before a judgment or decree for
payment of the money due has been obtained by the trustee, the holders of a
majority in principal amount of the outstanding debt

                                       9


securities of that series may rescind and annul the acceleration if all events
of default, other than the non-payment of accelerated principal and interest, if
any, with respect to debt securities of that series, have been cured or waived
as provided in the indenture. We refer you to the prospectus supplement relating
to any series of debt securities that are discount securities for the particular
provisions relating to acceleration of a portion of the principal amount of such
discount securities upon the occurrence of an event of default.

      The indenture provides that the trustee will be under no obligation to
exercise any of its rights or powers under the indenture at the request of any
holder of outstanding debt securities, unless the trustee receives indemnity
satisfactory to it against any loss, liability or expense. Subject to certain
rights of the trustee, the holders of a majority in principal amount of the
outstanding debt securities of any series will have the right to direct the
time, method and place of conducting any proceeding for any remedy available to
the trustee or exercising any trust or power conferred on the trustee with
respect to the debt securities of that series.

      No holder of any debt security of any series will have any right to
institute any proceeding, judicial or otherwise, with respect to the indenture
or for the appointment of a receiver or trustee, or for any remedy under the
indenture, unless:

      -     that holder has previously given to the trustee written notice of a
            continuing event of default with respect to debt securities of that
            series; and

      -     the holders of at least a majority in principal amount of the
            outstanding debt securities of that series have made written
            request, and offered reasonable indemnity, to the trustee to
            institute the proceeding as trustee, and the trustee has not
            received from the holders of a majority in principal amount of the
            outstanding debt securities of that series a direction inconsistent
            with that request and has failed to institute the proceeding within
            60 days.

      Notwithstanding the foregoing, the holder of any debt security will have
an absolute and unconditional right to receive payment of the principal of, and
any premium and interest on, that debt security on or after the due dates
expressed in that debt security and to institute suit for the enforcement of
payment.

      If any securities are outstanding under the indenture, the indenture
requires us, within 120 days after the end of our fiscal year, to furnish to the
trustee a statement as to compliance with the indenture. The indenture provides
that the trustee may withhold notice to the holders of debt securities of any
series of any default or event of default (except in payment on any debt
securities of that series) with respect to debt securities of that series if it
in good faith determines that withholding notice is in the interest of the
holders of those debt securities.

MODIFICATION AND WAIVER

      We may modify and amend the indenture with the consent of the holders of
at least a majority in principal amount of the outstanding debt securities of
each series affected by the modifications or amendments. We may not make any
modification or amendment without the consent of the holders of each affected
debt security then outstanding if that amendment will:

      -     reduce the amount of debt securities whose holders must consent to
            an amendment or waiver;

      -     reduce the rate of or extend the time for payment of interest
            (including default interest) on any debt security;

      -     reduce the principal of or premium on or change the fixed maturity
            of any debt security or reduce the amount of, or postpone the date
            fixed for, the payment of any sinking fund or analogous obligation
            with respect to any series of debt securities;

      -     reduce the principal amount of discount securities payable upon
            acceleration of maturity;

      -     waive a default in the payment of the principal of, or premium or
            interest on, any debt security (except a rescission of acceleration
            of the debt securities of any series by the holders of at least a
            majority in aggregate principal amount of the then outstanding debt
            securities of that series and a waiver of the payment default that
            resulted from such acceleration);

      -     make the principal of, or premium or interest on, any debt security
            payable in currency other than that stated in the debt security;

                                       10


      -     make any change to certain provisions of the indenture relating to,
            among other things, the right of holders of debt securities to
            receive payment of the principal of, and premium and interest on,
            those debt securities and to institute suit for the enforcement of
            any such payment and to waivers or amendments; or

      -     waive a redemption payment with respect to any debt security.

      Except for certain specified provisions, the holders of at least a
majority in principal amount of the outstanding debt securities of any series
may on behalf of the holders of all debt securities of that series waive our
compliance with provisions of the indenture. The holders of a majority in
principal amount of the outstanding debt securities of any series may on behalf
of the holders of all the debt securities of such series waive any past default
under the indenture with respect to that series and its consequences, except a
default in the payment of the principal of, or any premium or interest on, any
debt security of that series or in respect of a covenant or provision, which
cannot be modified or amended without the consent of the holder of each
outstanding debt security of the series affected; provided, however, that the
holders of a majority in principal amount of the outstanding debt securities of
any series may rescind an acceleration and its consequences, including any
related payment default that resulted from the acceleration.

DEFEASANCE OF DEBT SECURITIES AND CERTAIN COVENANTS IN CERTAIN CIRCUMSTANCES

      Legal Defeasance. The indenture provides that, unless otherwise provided
by the terms of the applicable series of debt securities, we may be discharged
from any and all obligations in respect of the debt securities of any series
(except for certain obligations to register the transfer or exchange of debt
securities of such series, to replace stolen, lost or mutilated debt securities
of such series, and to maintain paying agencies and certain provisions relating
to the treatment of funds held by paying agents). We will be so discharged upon
the deposit with the trustee, in trust, of money and/or U.S. government
obligations or, in the case of debt securities denominated in a single currency
other than U.S. dollars, foreign government obligations, that, through the
payment of interest and principal in accordance with their terms, will provide
money in an amount sufficient in the opinion of a nationally recognized firm of
independent public accountants to pay and discharge each installment of
principal of, premium and interest on and any mandatory sinking fund payments in
respect of the debt securities of that series on the stated maturity of those
payments in accordance with the terms of the indenture and those debt
securities.

      This discharge may occur only if, among other things, we have delivered to
the trustee an opinion of counsel stating that we have received from, or there
has been published by, the United States Internal Revenue Service a ruling or,
since the date of execution of the indenture, there has been a change in the
applicable United States federal income tax law, in either case to the effect
that, and based thereon such opinion shall confirm that, the holders of the debt
securities of that series will not recognize income, gain or loss for United
States federal income tax purposes as a result of the deposit, defeasance and
discharge and will be subject to United States federal income tax on the same
amounts and in the same manner and at the same times as would have been the case
if the deposit, defeasance and discharge had not occurred.

      Defeasance of Certain Covenants. The indenture provides that, unless
otherwise provided by the terms of the applicable series of debt securities,
upon compliance with certain conditions:

      -     we may omit to comply with the covenant described under the heading
            "Consolidation, Merger and Sale of Assets" and certain other
            covenants set forth in the indenture, as well as any additional
            covenants which may be set forth in the applicable prospectus
            supplement; and

      -     any omission to comply with those covenants will not constitute a
            default or an event of default with respect to the debt securities
            of that series, or covenant defeasance.

The conditions include:

      -     depositing with the trustee money and/or U.S. government obligations
            or, in the case of debt securities denominated in a single currency
            other than U.S. dollars, foreign government obligations, that,
            through the payment of interest and principal in accordance with
            their terms, will provide money in an amount sufficient in the
            opinion of a nationally recognized firm of independent public
            accountants to pay and discharge each installment of principal of,
            premium and interest on and any mandatory sinking fund payments in
            respect of the debt securities of that series on the stated maturity
            of those payments in accordance with the terms of the indenture and
            those debt securities; and

                                       11


      -     delivering to the trustee an opinion of counsel to the effect that
            the holders of the debt securities of that series will not recognize
            income, gain or loss for United States federal income tax purposes
            as a result of the deposit and related covenant defeasance and will
            be subject to United States federal income tax on the same amounts
            and in the same manner and at the same times as would have been the
            case if the deposit and related covenant defeasance had not
            occurred.

      Covenant Defeasance and Events of Default. In the event we exercise our
option to effect covenant defeasance with respect to any series of debt
securities and the debt securities of that series are declared due and payable
because of the occurrence of any event of default, the amount of money and/or
U.S. government obligations or foreign government obligations on deposit with
the trustee will be sufficient to pay amounts due on the debt securities of that
series at the time of their stated maturity but may not be sufficient to pay
amounts due on the debt securities of that series at the time of the
acceleration resulting from the event of default. In such a case, we would
remain liable for those payments.

      "Foreign Government Obligations" means, with respect to debt securities of
any series that are denominated in a currency other than U.S. dollars:

      -     direct obligations of the government that issued or caused to be
            issued such currency for the payment of which obligations its full
            faith and credit is pledged which are not callable or redeemable at
            the option of the issuer thereof; or

      -     obligations of a person controlled or supervised by or acting as an
            agency or instrumentality of that government the timely payment of
            which is unconditionally guaranteed as a full faith and credit
            obligation by that government which are not callable or redeemable
            at the option of the issuer thereof.

GOVERNING LAW

      The indenture and the debt securities will be governed by and construed in
accordance with the laws of the State of New York.

                             DESCRIPTION OF WARRANTS

      The following description, together with the additional information we may
include in any applicable prospectus supplements, summarizes the material terms
and provisions of the warrants that we may offer under this prospectus and the
related warrant agreements and warrant certificates. While the terms summarized
below will apply generally to any warrants that we may offer under this
prospectus, we will describe the particular terms of any series of warrants that
we may offer in more detail in the applicable prospectus supplement. If we
indicate in the prospectus supplement, the terms of any warrants offered under
that prospectus supplement may differ from the terms described below. However,
no prospectus supplement shall fundamentally change the terms that are set forth
in this prospectus or offer a security that is not registered and described in
this prospectus at the time of its effectiveness. Specific warrant agreements
will contain additional important terms and provisions and will be incorporated
by reference as an exhibit to the registration statement that includes this
prospectus or as an exhibit to a report filed under the Securities Exchange Act
of 1934.

GENERAL

        We will describe in the applicable prospectus supplement the terms of
the series of warrants, including:

      -     the offering price and aggregate number of warrants offered;

      -     the currency for which the warrants may be purchased;

      -     if applicable, the designation and terms of the securities with
            which the warrants are issued and the number of warrants issued with
            each such security or each principal amount of such security;

      -     if applicable, the date on and after which the warrants and the
            related securities will be separately transferable;

      -     in the case of warrants to purchase common stock or preferred stock,
            the number of shares of common stock or preferred stock, as the case
            may be, purchasable upon the exercise of one warrant and the price
            at which these shares may be purchased upon such exercise;

                                       12


      -     in the case of warrants to purchase debt securities, the principal
            amount of debt securities purchasable upon exercise of one warrant
            and the price at, and currency in which, this principal amount of
            debt securities may be purchased upon such exercise;

      -     the effect of any merger, consolidation, sale or other disposition
            of our business on the warrant agreements and the warrants;

      -     the terms of any rights to redeem or call the warrants;

      -     any provisions for changes to or adjustments in the exercise price
            or number of securities issuable upon exercise of the warrants;

      -     the dates on which the right to exercise the warrants will commence
            and expire;

      -     the manner in which the warrant agreements and warrants may be
            modified;

      -     federal income tax consequences of holding or exercising the
            warrants;

      -     the terms of the securities issuable upon exercise of the warrants;
            and

      -     any other specific terms, preferences, rights or limitations of or
            restrictions on the warrants.

      Before exercising their warrants, holders of warrants will not have any of
the rights of holders of the securities purchasable upon such exercise,
including:

      -     in the case of warrants to purchase common stock or preferred stock,
            the right to receive dividends, if any, or, payments upon our
            liquidation, dissolution or winding up or to exercise voting rights,
            if any; or

      -     in the case of warrants to purchase debt securities, the right to
            receive payments of principal of, or premium, if any, or interest
            on, the debt securities purchasable upon exercise or to enforce
            covenants in the applicable indenture.

EXERCISE OF WARRANTS

      Each warrant will entitle the holder to purchase the securities that we
specify in the applicable prospectus supplement at the exercise price that we
describe in the applicable prospectus supplement. Unless we otherwise specify in
the applicable prospectus supplement, holders of the warrants may exercise the
warrants at any time up to the specified time on the expiration date that we set
forth in the applicable prospectus supplement. After the close of business on
the expiration date, unexercised warrants will become void.

      Holders of the warrants may exercise the warrants by delivering the
warrant certificate representing the warrants to be exercised together with
specified information, and paying the required amount to the warrant agent in
immediately available funds, as provided in the applicable prospectus
supplement. We will set forth on the reverse side of the warrant certificate and
in the applicable prospectus supplement the information that the holder of the
warrant will be required to deliver to the warrant agent.

      Upon receipt of the required payment and the warrant certificate properly
completed and duly executed at the corporate trust office of the warrant agent
or any other office indicated in the applicable prospectus supplement, we will
issue and deliver the securities purchasable upon such exercise. If fewer than
all of the warrants represented by the warrant certificate are exercised, then
we will issue a new warrant certificate for the remaining amount of warrants. If
we so indicate in the applicable prospectus supplement, holders of the warrants
may surrender securities as all or part of the exercise price for warrants.

GOVERNING LAW

      The warrants and warrant agreements will be governed by and construed in
accordance with the laws of the State of New York.

ENFORCEABILITY OF RIGHTS BY HOLDERS OF WARRANTS

      Each warrant agent will act solely as our agent under the applicable
warrant agreement and will not assume any obligation or relationship of agency
or trust with any holder of any warrant. A single bank or trust company may act
as warrant agent for more than one issue of warrants. A warrant agent will have
no duty or responsibility in case of

                                       13


any default by us under the applicable warrant agreement or warrant, including
any duty or responsibility to initiate any proceedings at law or otherwise, or
to make any demand upon us. Any holder of a warrant may, without the consent of
the related warrant agent or the holder of any other warrant, enforce by
appropriate legal action its right to exercise, and receive the securities
purchasable upon exercise of, its warrants.

                              DESCRIPTION OF UNITS

      The following description, together with the additional information we may
include in any applicable prospectus supplements, summarizes the material terms
and provisions of the units that we may offer under this prospectus and the
related unit agreements. While the terms summarized below will apply generally
to any units that we may offer under this prospectus, we will describe the
particular terms of any series of units that we may offer in more detail in the
applicable prospectus supplement. If we indicate in the prospectus supplement,
the terms of any units offered under that prospectus supplement may differ from
the terms described below. However, no prospectus supplement shall fundamentally
change the terms that are set forth in this prospectus or offer a security that
is not registered and described in this prospectus at the time of its
effectiveness. Specific unit agreements will contain additional important terms
and provisions and will be incorporated by reference as an exhibit to the
registration statement that includes this prospectus or as an exhibit to a
report filed under the Securities Exchange Act of 1934.

GENERAL

      We may issue units comprised of one or more shares of common stock, shares
of preferred stock, debt securities and warrants in any combination. Each unit
will be issued so that the holder of the unit is also the holder of each
security included in the unit. Thus, the holder of a unit will have the rights
and obligations of a holder of each included security. The unit agreement under
which a unit is issued may provide that the securities included in the unit may
not be held or transferred separately, at any time or at any time before a
specified date.

      We will describe in the applicable prospectus supplement the terms of the
series of units, including:

      -     the designation and terms of the units and of the securities
            comprising the units, including whether and under what circumstances
            those securities may be held or transferred separately;

      -     any provisions of the governing unit agreement that differ from
            those described below; and

      -     any provisions for the issuance, payment, settlement, transfer or
            exchange of the units or of the securities comprising the units.

      The provisions described in this section, as well as those described under
"Description of Capital Stock," "Description of Debt Securities" and
"Description of Warrants" will apply to each unit and to any common stock,
preferred stock, debt security or warrant included in each unit, respectively.

ISSUANCE IN SERIES

      We may issue units in such amounts and in numerous distinct series as we
determine.

ENFORCEABILITY OF RIGHTS BY HOLDERS OF UNITS

      Each unit agent will act solely as our agent under the applicable unit
agreement and will not assume any obligation or relationship of agency or trust
with any holder of any unit. A single bank or trust company may act as unit
agent for more than one series of units. A unit agent will have no duty or
responsibility in case of any default by us under the applicable unit agreement
or unit, including any duty or responsibility to initiate any proceedings at law
or otherwise, or to make any demand upon us. Any holder of a unit may, without
the consent of the related unit agent or the holder of any other unit, enforce
by appropriate legal action its rights as holder under any security included in
the unit.

TITLE

      Lexicon, the unit agents and any of their agents may treat the registered
holder of any unit certificate as an absolute owner of the units evidenced by
that certificate for any purpose and as the person entitled to exercise the
rights attaching to the units so requested, despite any notice to the contrary.
See "Legal Ownership of Securities."

                                       14


                          LEGAL OWNERSHIP OF SECURITIES

      We can issue securities in registered form or in the form of one or more
global securities. We describe global securities in greater detail below. We
refer to those persons who have securities registered in their own names on the
books that we or any applicable trustee maintain for this purpose as the
"holders" of those securities. These persons are the legal holders of the
securities. We refer to those persons who, indirectly through others, own
beneficial interests in securities that are not registered in their own names,
as "indirect holders" of those securities. As we discuss below, indirect holders
are not legal holders, and investors in securities issued in book-entry form or
in street name will be indirect holders.

BOOK-ENTRY HOLDERS

      We may issue securities in book-entry form only, as we will specify in the
applicable prospectus supplement. This means securities may be represented by
one or more global securities registered in the name of a financial institution
that holds them as depositary on behalf of other financial institutions that
participate in the depositary's book-entry system. These participating
institutions, which are referred to as participants, in turn, hold beneficial
interests in the securities on behalf of themselves or their customers.

      Only the person in whose name a security is registered is recognized as
the holder of that security. Securities issued in global form will be registered
in the name of the depositary or its nominee. Consequently, for securities
issued in global form, we will recognize only the depositary as the holder of
the securities, and we will make all payments on the securities to the
depositary. The depositary passes along the payments it receives to its
participants, which in turn pass the payments along to their customers who are
the beneficial owners. The depositary and its participants do so under
agreements they have made with one another or with their customers; they are not
obligated to do so under the terms of the securities.

      As a result, investors in a book-entry security will not own securities
directly. Instead, they will own beneficial interests in a global security,
through a bank, broker or other financial institution that participates in the
depositary's book-entry system or holds an interest through a participant. As
long as the securities are issued in global form, investors will be indirect
holders, and not holders, of the securities.

STREET NAME HOLDERS

      We may terminate a global security or issue securities in non-global form.
In these cases, investors may choose to hold their securities in their own names
or in "street name." Securities held by an investor in street name would be
registered in the name of a bank, broker or other financial institution that the
investor chooses, and the investor would hold only a beneficial interest in
those securities through an account he or she maintains at that institution.

      For securities held in street name, we will recognize only the
intermediary banks, brokers and other financial institutions in whose names the
securities are registered as the holders of those securities, and we will make
all payments on those securities to them. These institutions pass along the
payments they receive to their customers who are the beneficial owners, but only
because they agree to do so in their customer agreements or because they are
legally required to do so. Investors who hold securities in street name will be
indirect holders, not holders, of those securities.

LEGAL HOLDERS

      Our obligations, as well as the obligations of any applicable trustee and
of any third parties employed by us or a trustee, run only to the legal holders
of the securities. We do not have obligations to investors who hold beneficial
interests in global securities, in street name or by any other indirect means.
This will be the case whether an investor chooses to be an indirect holder of a
security or has no choice because we are issuing the securities only in global
form.

      For example, once we make a payment or give a notice to the holder, we
have no further responsibility for the payment or notice even if that holder is
required, under agreements with depositary participants or customers or by law,
to pass it along to the indirect holders but does not do so. Similarly, we may
want to obtain the approval of the holders to amend an indenture, to relieve us
of the consequences of a default or of our obligation to comply with a
particular provision of the indenture or for other purposes. In such an event,
we would seek approval only from the holders, and not the indirect holders, of
the securities. Whether and how the holders contact the indirect holders is up
to the holders.

                                       15


SPECIAL CONSIDERATIONS FOR INDIRECT HOLDERS

      If you hold securities through a bank, broker or other financial
institution, either in book-entry form or in street name, you should check with
your own institution to find out:

      -     how it handles securities payments and notices;

      -     whether it imposes fees or charges;

      -     how it would handle a request for the holders' consent, if ever
            required;

      -     whether and how you can instruct it to send you securities
            registered in your own name so you can be a holder, if that is
            permitted in the future;

      -     how it would exercise rights under the securities if there were a
            default or other event triggering the need for holders to act to
            protect their interests; and

      -     if the securities are in book-entry form, how the depositary's rules
            and procedures will affect these matters.

GLOBAL SECURITIES

      A global security is a security that represents one or any other number of
individual securities held by a depositary. Generally, all securities
represented by the same global securities will have the same terms.

      Each security issued in book-entry form will be represented by a global
security that we deposit with and register in the name of a financial
institution or its nominee that we select. The financial institution that we
select for this purpose is called the depositary. Unless we specify otherwise in
the applicable prospectus supplement, The Depository Trust Company, New York,
New York, known as DTC, will be the depositary for all securities issued in
book-entry form.

      A global security may not be transferred to or registered in the name of
anyone other than the depositary, its nominee or a successor depositary, unless
special termination situations arise. We describe those situations below under
"Special Situations When a Global Security Will Be Terminated." As a result of
these arrangements, the depositary, or its nominee, will be the sole registered
owner and holder of all securities represented by a global security, and
investors will be permitted to own only beneficial interests in a global
security. Beneficial interests must be held by means of an account with a
broker, bank or other financial institution that in turn has an account with the
depositary or with another institution that does. Thus, an investor whose
security is represented by a global security will not be a holder of the
security, but only an indirect holder of a beneficial interest in the global
security.

      If the prospectus supplement for a particular security indicates that the
security will be issued in global form only, then the security will be
represented by a global security at all times unless and until the global
security is terminated. If termination occurs, we may issue the securities
through another book-entry clearing system or decide that the securities may no
longer be held through any book-entry clearing system.

SPECIAL CONSIDERATIONS FOR GLOBAL SECURITIES

      As an indirect holder, an investor's rights relating to a global security
will be governed by the account rules of the investor's financial institution
and of the depositary, as well as general laws relating to securities transfers.
We do not recognize an indirect holder as a holder of securities and instead
deal only with the depositary that holds the global security.

      If securities are issued only in the form of a global security, an
investor should be aware of the following:

      -     An investor cannot cause the securities to be registered in his or
            her name, and cannot obtain non-global certificates for his or her
            interest in the securities, except in the special situations we
            describe below;

      -     An investor will be an indirect holder and must look to his or her
            own bank or broker for payments on the securities and protection of
            his or her legal rights relating to the securities, as we describe
            above;

      -     An investor may not be able to sell interests in the securities to
            some insurance companies and to other institutions that are required
            by law to own their securities in non-book-entry form;

                                       16


      -     An investor may not be able to pledge his or her interest in a
            global security in circumstances where certificates representing the
            securities must be delivered to the lender or other beneficiary of
            the pledge in order for the pledge to be effective;

      -     The depositary's policies, which may change from time to time, will
            govern payments, transfers, exchanges and other matters relating to
            an investor's interest in a global security. We and any applicable
            trustee have no responsibility for any aspect of the depositary's
            actions or for its records of ownership interests in a global
            security. We and the trustee also do not supervise the depositary in
            any way;

      -     The depositary may, and we understand that DTC will, require that
            those who purchase and sell interests in a global security within
            its book-entry system use immediately available funds, and your
            broker or bank may require you to do so as well; and

      -     Financial institutions that participate in the depositary's
            book-entry system, and through which an investor holds its interest
            in a global security, may also have their own policies affecting
            payments, notices and other matters relating to the securities.
            There may be more than one financial intermediary in the chain of
            ownership for an investor. We do not monitor and are not responsible
            for the actions of any of those intermediaries.

SPECIAL SITUATIONS WHEN A GLOBAL SECURITY WILL BE TERMINATED

      In a few special situations described below, the global security will
terminate and interests in it will be exchanged for physical certificates
representing those interests. After that exchange, the choice of whether to hold
securities directly or in street name will be up to the investor. Investors must
consult their own banks or brokers to find out how to have their interests in
securities transferred to their own name, so that they will be direct holders.
We have described the rights of holders and street name investors above.

      The global security will terminate when the following special situations
occur:

      -     if the depositary notifies us that it is unwilling, unable or no
            longer qualified to continue as depositary for that global security
            and we do not appoint another institution to act as depositary
            within 90 days;

      -     if we notify any applicable trustee that we wish to terminate that
            global security; or

      -     if an event of default has occurred with regard to securities
            represented by that global security and has not been cured or
            waived.

      The prospectus supplement may also list additional situations for
terminating a global security that would apply only to the particular series of
securities covered by the prospectus supplement. When a global security
terminates, the depositary, and not we or any applicable trustee, is responsible
for deciding the names of the institutions that will be the initial direct
holders.

                SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

      This prospectus and the documents incorporated by reference into this
prospectus contain certain information regarding our financial projections,
plans and strategies that are forward-looking statements within the meaning of
Section 27A of the Securities Act of 1933 and 21E of the Securities Exchange Act
of 1934. We have attempted to identify forward-looking statements by terminology
including "anticipate," "believe," "can," "continue," "could," "estimate,"
"expect," "intend," "may," "plan," "potential," "predict," "should" or "will" or
the negative of these terms or other comparable terminology. These statements,
which are only predictions and involve known and unknown risks, uncertainties
and other important factors may include, among other things, statements which
address our strategy and operating performance, events or developments that we
expect or anticipate will occur in the future, such as projections of our future
results of operations or of our financial condition, the status of any
collaborative agreements, our research and development efforts and anticipated
trends in our business.

        We have based these forward-looking statements on our current
expectations and projections about future events. However, there may be events
in the future that we are not able to predict accurately or which we do not
fully control that could cause actual results to differ materially from those
expressed or implied in our forward-looking statements. Many important factors
could cause actual results to differ materially from those expressed or implied
by these forward-looking statements, including those discussed under "Risk
Factors" in this prospectus and any prospectus supplement and other sections of
the documents incorporated by reference into this prospectus. We

                                       17


undertake no obligation to publicly release any revisions to the forward-looking
statements or reflect events or circumstances after the date of this prospectus.

                       RATIO OF EARNINGS TO FIXED CHARGES

      Our earnings were insufficient to cover fixed charges in each of the years
in the five-year period ended December 31, 2003 and in the nine-month period
ended September 30, 2004. "Fixed charges" consist of interest expense, the
estimated interest included in rental expense and accretion on redeemable
convertible preferred stock. The following table sets forth the computation of
our ratio of earnings to fixed charges for the periods indicated:



                                            NINE MONTHS
                                               ENDED                            FISCAL YEARS ENDED DECEMBER 31,
                                            SEPTEMBER 30,           ---------------------------------------------------
                                                2004                2003        2002       2001       2000        1999
                                            ----------              ----        ----       ----       ----        ----
                                                                                                
Ratio of earnings to fixed charges (1)          -                     -           -          -         -            -


----------------
(1)   For the nine months ended September 30, 2004, and the fiscal years ended
      December 31, 2003, 2002, 2001, 2000 and 1999, our earnings were
      insufficient to cover fixed charges by $46.6 million, $61.1 million, $59.7
      million, $35.2 million, $26.1 million, and $13.0 million, respectively.

      For the periods indicated above, we had no outstanding shares of preferred
stock with required dividend payments. Therefore, our ratios of earnings to
combined fixed charges and preferred stock dividends for the periods indicated
are identical to the ratios presented in the table above.

                                 USE OF PROCEEDS

      Except as otherwise described in the prospectus supplement relating to an
offering, we intend to use the net proceeds from the sale(s) of securities
offered pursuant to this prospectus and any prospectus supplement for research
and development and general corporate purposes, including capital expenditures
and working capital needs. We may also use some or all of the net proceeds to
acquire or invest in businesses, products and technologies that are
complementary to our own.

      The amounts that we actually expend for working capital purposes,
investments or acquisitions will vary significantly depending on a number of
factors, including future revenue growth, if any, the amount of cash we generate
from operations and the progress of our product development efforts.
Accordingly, our management will retain broad discretion in the allocation of
the net proceeds from the sale(s) of the offered securities. If we elect at the
time of the issuance of the securities to make different or more specific use of
proceeds other than as described in this prospectus, the change in use of
proceeds will be described in the applicable prospectus supplement.

                              PLAN OF DISTRIBUTION

      We may sell securities under this prospectus from time to time in any one
or more of the following ways:

      -     to or through underwriters;

      -     through brokers or dealers;

      -     directly to other purchasers; or

      -     through agents.

        We may sell securities under this prospectus from time to time in one or
more transactions:

      -     at a fixed price or prices, which may be changed;

      -     at market prices prevailing at the time of sale;

      -     at prices related to such prevailing market prices; or

      -     at negotiated prices.

                                       18


      The prospectus supplement relating to the securities will set forth the
terms of the offering of such securities, including the name or names of any
underwriters, brokers, dealers or agents, the name or names of any managing
underwriter or underwriters, the purchase price of the securities and the net
proceeds to us from such sale, any delayed delivery arrangements, any
underwriting discounts and commissions and other items constituting
underwriters' compensation, any public offering price, any discounts or
concessions allowed or reallowed or paid to dealers, any commissions paid to
agents and any securities exchange or market on which the securities may be
listed.

      If we use underwriters in the sale of securities, the underwriters will
acquire the securities for their own account. The underwriters may resell the
securities from time to time in one or more transactions, including negotiated
transactions, at a fixed public offering price or at varying prices determined
at the time of sale. Underwriters may offer securities to the public either
through underwriting syndicates represented by one or more managing underwriters
or directly by one or more firms acting as underwriters. Unless we inform you
otherwise in the prospectus supplement, the obligations of the underwriters to
purchase the securities will be subject to certain conditions, and the
underwriters will be obligated to purchase all of the offered securities if they
purchase any of them. The underwriters may change from time to time any public
offering price and any discounts or concessions allowed or reallowed or paid to
dealers.

      In connection with the sale of our securities, underwriters, brokers,
dealers or agents may receive compensation from us or purchasers of securities
for whom they may act as agents, in the form of discounts, concessions or
commissions. Underwriters, dealers and agents that participate in the
distribution of our securities may be deemed to be underwriters, and any
discounts or commissions received by them from us and any profit on the resale
of securities by them may be deemed to be underwriting discounts and commissions
under the Securities Act of 1933. Any person who may be deemed to be an
underwriter will be identified, and the compensation received from us will be
described, in the prospectus supplement.

      During and after an offering through underwriters, the underwriters may
purchase and sell the securities in the open market. These transactions may
include over-allotment and stabilizing transactions and purchases to cover
syndicate short positions created in connection with the offering. The
underwriters may also impose a penalty bid, whereby selling concessions allowed
to syndicate members or other broker-dealers for the securities sold for their
account may be reclaimed by the syndicate if those securities are repurchased by
the syndicate in stabilizing or covering transactions. These activities may
stabilize, maintain or otherwise affect the market price of the securities,
which may be higher than the price that might otherwise prevail in the open
market, and, if commenced, may be discontinued at any time.

      If dealers or brokers acting as dealers are used in the sale of the
securities, we will sell the securities to such dealers or brokers as
principals. The dealers or brokers acting as dealers may then resell such
securities to the public at varying prices to be determined by such dealers or
brokers at the time of resale. The names of dealers or brokers acting as dealers
and the terms of the transaction will be set forth in the prospectus supplement
relating to such securities. We may sell the securities directly or through
agents designated by us from time to time. Any agent involved in the offer or
sale of the securities will be named, and any commissions that we pay to such
agent will be set forth, in the prospectus supplement relating to such
securities. Unless otherwise indicated in the prospectus supplement, any such
agent will be acting on a best efforts basis for the period of its appointment.

      We may sell securities directly, in which case no underwriters or agents
would be involved. We may sell securities directly to institutional investors or
others who may be deemed to be underwriters within the meaning of the Securities
Act of 1933 with respect to any sale of those securities.

      All securities we offer, other than common stock and other securities
issued upon a reopening of a previous series, will be new issues of securities
with no established trading market. Any underwriters may make a market in these
securities, but will not be obligated to do so and may discontinue any market
making at any time without notice. We cannot guarantee the liquidity of the
trading markets for any securities.

      If so indicated in the prospectus supplement, we will authorize agents,
underwriters, brokers or dealers to solicit offers from certain types of
institutions to purchase securities at the public offering price set forth in
the prospectus supplement pursuant to delayed delivery contracts providing for
payment and delivery on a specified date in the future. Such contracts will be
subject only to those conditions set forth in the prospectus supplement, and the
prospectus supplement will set forth also the commission payable for
solicitation of such contracts.

                                       19


      We may have agreements with the underwriters, dealers and agents to
indemnify them against specific civil liabilities, including liabilities under
the Securities Act of 1933, or to contribute with respect to payments which the
underwriters, dealers or agents may be required to make as a result of those
specific civil liabilities.

      Underwriters and agents and their affiliates may be customers of, engage
in transactions with, or perform services for us or our subsidiaries in the
ordinary course of their businesses.

                                  LEGAL MATTERS

      The validity of the issuance of the securities offered by this prospectus
has been passed upon for us by Vinson & Elkins L.L.P., Houston, Texas.

                                     EXPERTS

      The consolidated financial statements of Lexicon Genetics Incorporated
included in our annual report on Form 10-K for the years ended December 31, 2003
and 2002 have been audited by Ernst & Young LLP, independent registered public
accounting firm, as set forth in their report thereon (which contains one
explanatory paragraph describing the audit procedures relating to a revision to
the 2001 financial statements for a reclassification adjustment that was applied
to revise the 2001 financial statements described in Note 4 to the consolidated
financial statements; the 2001 financial statements were audited by other
auditors who have ceased operations and for which Ernst & Young LLP has
expressed no opinion or other form of assurance on the 2001 financial statements
taken as a whole), included therein and incorporated herein by reference. Such
consolidated financial statements are incorporated herein by reference in
reliance upon such report given on the authority of such firm as experts in
accounting and auditing.

      The financial statements for the year ended December 31, 2001,
incorporated by reference in this prospectus, have been audited by Arthur
Andersen LLP, independent public accountants, as indicated in their report with
respect thereto, and are included herein in reliance upon the authority of said
firm as experts in accounting and auditing. Arthur Andersen LLP has not
consented to the inclusion of their report in this prospectus, and we have not
obtained their consent to do so in reliance upon Rule 437a of the Securities Act
of 1933. Because Arthur Andersen LLP has not consented to the inclusion of their
report in this prospectus, you will not be able to recover against Arthur
Andersen LLP under Section 11(a) of the Securities Act for any untrue statement
of a material fact contained in the financial statements audited by Arthur
Andersen LLP or any omission to state a material fact required to be stated
therein.

                       WHERE YOU CAN FIND MORE INFORMATION

      We have filed with the Securities and Exchange Commission a registration
statement on Form S-3 under the Securities Act of 1933 regarding the offer and
sale of securities under this prospectus. This prospectus, which constitutes a
part of the registration statement, does not contain all of the information
contained in the registration statement or the exhibits to the registration
statement, as permitted by the rules and regulations of the SEC. For further
information about us and our securities, please review the registration
statement and the exhibits filed as a part of it. Statements made in this
prospectus that describe documents may not necessarily be complete. We recommend
that you review the documents that we have filed with the registration statement
to obtain a more complete understanding of these documents. A copy of the
registration statement, including the exhibits filed as a part of it, may be
inspected without charge at the SEC's Public Reference Room, 450 Fifth Street,
N.W., Washington, D.C. 20549, and copies of all or any part of the registration
statement may be obtained from the SEC upon the payment of fees prescribed by
it. You may obtain information on the Public Reference Room by calling the SEC
at 1-800-SEC-0330. The SEC maintains a Web site at http://www.sec.gov that
contains reports, proxy and information statements and other information
regarding companies that file electronically with it.

      We are subject to the information and reporting requirements of the
Securities Exchange Act of 1934 and will file periodic reports, proxy statements
and other information with the SEC. You may inspect any of these documents as
described in the preceding paragraph. These reports, proxy statements and other
information may also be inspected at the offices of Nasdaq Operations, 1735 K
Street, N.W., Washington, D.C. 20006.

                       DOCUMENTS INCORPORATED BY REFERENCE

      The Securities and Exchange Commission allows us to "incorporate by
reference" into this prospectus information that we file with the SEC in other
documents. This means that we can disclose important information to

                                       20


you by referring to other documents that contain that information. The
information incorporated by reference is considered to be part of this
prospectus, except for information superseded by information in this prospectus.
We incorporate by reference the documents listed below that we have previously
filed with the SEC and any future filings we make with the SEC under Sections
13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934 (other than
information furnished to the SEC under Item 2.02 (or previous Item 12) of Form
8-K), prior to the termination of the offering of the securities covered by this
prospectus:

      -     our annual report on Form 10-K for the year ended December 31, 2003;

      -     our amendment to our annual report on Form 10-K/A for the year ended
            December 31, 2003, as filed on July 16, 2004;

      -     our quarterly reports on Form 10-Q for the quarterly periods ended
            March 31, June 30 and September 30, 2004;

      -     our current reports on Form 8-K dated April 21, November 2 and
            December 23, 2004; and

      -     the description of our common stock contained in our registration
            statement on Form 8-A filed with the Commission on March 27, 2000
            pursuant to Section 12 of the Securities Exchange Act of 1934,
            including any amendments and reports filed for the purpose of
            updating such description.

      Any statement contained in a document incorporated or deemed to be
incorporated by reference in this prospectus will be deemed to be modified or
superseded for purposes of this prospectus to the extent that a statement
contained in this prospectus or in any other subsequently filed document which
also is or is deemed to be incorporated by reference in this prospectus modifies
or supersedes that statement. Any statement that is modified or superseded will
not constitute a part of this prospectus, except as so modified or superseded.
You may rely on any statement contained in this prospectus or in documents
incorporated or deemed to be incorporated in this prospectus, unless that
statement has been subsequently modified or superseded as described above prior
to the time you make your investment decision.

        Upon your written or oral request, we will provide you at no cost a copy
of any or all of the documents incorporated by reference in this prospectus,
other than the exhibits to those documents, unless the exhibits are specifically
incorporated by reference into this prospectus. You may request a copy of these
documents by contacting:

            Investor Relations
            Lexicon Genetics Incorporated
            8800  Technology Forest Place
            The   Woodlands, Texas 77381-1160
            Telephone: (281) 863-3000

      YOU SHOULD RELY ONLY ON THE INFORMATION CONTAINED IN THIS PROSPECTUS AND
DOCUMENTS INCORPORATED INTO THIS PROSPECTUS BY REFERENCE. WE HAVE NOT AUTHORIZED
ANYONE TO PROVIDE YOU WITH INFORMATION DIFFERENT FROM THAT CONTAINED IN THIS
PROSPECTUS OR THE DOCUMENTS INCORPORATED BY REFERENCE HEREIN. THIS PROSPECTUS
MAY ONLY BE USED WHERE IT IS LEGAL TO SELL THESE SECURITIES. THE INFORMATION
CONTAINED IN THIS PROSPECTUS, THE DOCUMENTS INCORPORATED BY REFERENCE HEREIN AND
ANY SUPPLEMENTS TO THIS PROSPECTUS IS ACCURATE ONLY AS OF THE DATES OF THEIR
RESPECTIVE COVERS OR EARLIER DATES AS SPECIFIED THEREIN, REGARDLESS OF THE TIME
OF DELIVERY OF THIS PROSPECTUS OR ANY SUPPLEMENT TO THIS PROSPECTUS OR OF ANY
SALE OF OUR SECURITIES.

      In this prospectus, "Lexicon," "Lexicon Genetics," "we," "us" and "our"
refer to Lexicon Genetics Incorporated and its subsidiaries.

      The Lexicon name and logo, LexVision(R) and OmniBank(R) are registered
trademarks and Genome5000(TM) and e-Biology(TM) are trademarks of Lexicon
Genetics Incorporated.

                                       21


                                     PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM  14. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION.

      The estimated expenses payable by the Registrant in connection with the
issuance and distribution of the securities being registered (other than
underwriting discounts and commissions) are as follows:


                                
SEC Registration Fee .........     $ 17,655
Printing Expenses ............       50,000
Accounting Fees and Expenses .       35,000
Legal Fees and Expenses ......      100,000
Transfer Agent and Registrar Fees     3,000
Miscellaneous Expenses .......        4,345
                                   --------
          Total ..............     $210,000
                                   ========


ITEM  15. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

      Section 145 of the Delaware General Corporation Law ("DGCL") provides that
a corporation may indemnify any person who was or is a party or is threatened to
be made a party to any threatened, pending or completed action, suit or
proceeding whether civil, criminal, administrative or investigative (other than
an action by or in the right of the corporation) by reason of the fact that he
is or was a director, officer, employee or agent of the corporation, or is or
was serving at the request of the corporation as a director, officer, employee
or agent of another corporation, partnership, joint venture, trust or other
enterprise, against expenses (including attorneys' fees), judgments, fines and
amounts paid in settlement actually and reasonably incurred by him in connection
with such action, suit or proceeding if he acted in good faith and in a manner
he reasonably believed to be in or not opposed to the best interests of the
corporation, and, with respect to any criminal action or proceeding, had no
reasonable cause to believe his conduct was unlawful. Section 145 further
provides that a corporation similarly may indemnify any such person serving in
any such capacity who was or is a party or is threatened to be made a party to
any threatened, pending or completed action or suit by or in the right of the
corporation to procure a judgment in its favor by reason of the fact that he is
or was a director, officer, employee or agent of the corporation or is or was
serving at the request of the corporation as a director, officer, employee or
agent of another corporation, partnership, joint venture, trust or other
enterprise, against expenses (including attorneys' fees) actually and reasonably
incurred in connection with the defense or settlement of such action or suit if
he acted in good faith and in a manner he reasonably believed to be in or not
opposed to the best interests of the corporation and except that no
indemnification shall be made in respect of any claim, issue or matter as to
which such person shall have been adjudged to be liable to the corporation
unless and only to the extent that the Delaware Court of Chancery or such other
court in which such action or suit was brought shall determine upon application
that, despite the adjudication of liability but in view of all of the
circumstances of the case, such person is fairly and reasonably entitled to
indemnity for such expenses which the Delaware Court of Chancery or such other
court shall deem proper.

      Lexicon's certificate of incorporation and bylaws provide that
indemnification shall be to the fullest extent permitted by the DGCL for all
current or former directors or officers. As permitted by the DGCL, the restated
certificate of incorporation provides that directors of Lexicon shall have no
personal liability to Lexicon or its stockholders for monetary damages for
breach of fiduciary duty as a director, except (1) for any breach of the
director's duty of loyalty to Lexicon or its stockholders, (2) for acts or
omissions not in good faith or which involve intentional misconduct or knowing
violation of law, (3) under Section 174 of the DGCL or (4) for any transaction
from which a director derived an improper personal benefit.

      Lexicon has entered into indemnification agreements with each of its
officers and directors. These agreements, among other things, require Lexicon to
indemnify each officer and director for all expenses, including attorneys' fees,
liabilities, judgments, fines, penalties, excise taxes and settlement amounts
incurred by any such person in any claim, action, suit or proceeding, including
any action by or in the right of Lexicon, arising out of the person's services
as a director, officer, employee, agent or fiduciary to Lexicon, any subsidiary
of Lexicon or to any other company or enterprise for which the person provides
services at Lexicon's request.

                                      II-1


      At present, there is no pending litigation or proceeding involving a
director or officer of Lexicon as to which indemnification is being sought nor
is Lexicon aware of any threatened litigation that may result in claims for
indemnification by any officer or director.

ITEM  16. EXHIBITS.



 EXHIBIT NO.                                                  DESCRIPTION
-------------     -----------------------------------------------------------------------------------------------------------
               
 *1.1      --     Form of Underwriting Agreement.
  3.1      --     Restated Certificate of Incorporation (filed as Exhibit 3.1 to the Company's Registration Statement on
                   Form S-1 (Registration No. 333-96469) and incorporated by reference herein).
  3.2      --     Restated Bylaws (filed as Exhibit 3.2 to the Company's Registration Statement on
                   Form S-1 (Registration No. 333-96469) and incorporated by reference herein).
  4.1      --     Amended and Restated Registration Rights Agreement dated as of May 7, 1998 by and among the Company and the
                   stockholders named therein (filed as Exhibit 4.1 to the Company's Registration Statement on Form S-3
                   (Registration No. 333-67294) and incorporated by reference herein).
 *4.2      --     Form of Certificate of Designation of Preferred Stock.
  4.3      --     Form of Indenture.
 *4.4      --     Form of Note.
 *4.5      --     Form of Common Stock Warrant Agreement and Warrant Certificate.
 *4.6      --     Form of Preferred Stock Warrant Agreement and Warrant Certificate.
 *4.7      --     Form of Debt Securities Warrant Agreement and Warrant Certificate.
 *4.8      --     Form of Unit Agreement.
  5.1      --     Opinion of Vinson & Elkins L.L.P.
 12.1      --     Statement of Computation of Ratio of Earnings to Fixed Charges.
 23.1      --     Consent of Ernst & Young LLP.
 23.2      --     Consent of Vinson & Elkins L.L.P. (contained in Exhibit 5.1).
 24.1      --     Power of Attorney (contained in signature page).
*25.1      --     Statement of Eligibility of Trustee under the Indenture.


----------

*     To be filed by amendment, as an exhibit to a report filed under the
      Securities Exchange Act of 1934, as amended, or as otherwise required by
      regulation of the Securities and Exchange Commission, and incorporated by
      reference herein.

ITEM  17. UNDERTAKINGS.

      The   undersigned Registrant hereby undertakes:

                  (a) To file, during any period in which offers or sales are
            being made, a post-effective amendment to this Registration
            Statement:

                        (i) to include any prospectus required by Section
                  10(a)(3) of the Securities Act of 1933, as amended (the
                  "Securities Act");

                        (ii) to reflect in the prospectus any facts or events
                  arising after the effective date of this Registration
                  Statement (or the most recent post-effective amendment
                  thereof) which, individually or in the aggregate, represent a
                  fundamental change in the information set forth in this
                  Registration Statement. Notwithstanding the foregoing, any
                  increase or decrease in the volume of securities offered (if
                  the total dollar value of securities offered would not exceed
                  that which was registered) and any deviation from the low or
                  high end of the estimated maximum offering range may be
                  reflected in the form of prospectus filed with the Commission
                  pursuant to Rule 424(b) if, in the aggregate, the changes in
                  volume and price represent no more than a 20 percent change in
                  the maximum aggregate offering price set forth in the
                  "Calculation of Registration Fee" table in the effective
                  Registration Statement; and

                        (iii) to include any material information with respect
                  to the plan of distribution not previously disclosed in this
                  Registration Statement or any material change to such
                  information in this Registration Statement;

                                      II-2


                  provided, however, that paragraphs (a)(i) and (a)(ii) do not
                  apply if the information required to be included in a
                  post-effective amendment by those paragraphs is contained in
                  periodic reports filed by the Registrant pursuant to Section
                  13 or Section 15(d) of the Securities Exchange Act of 1934, as
                  amended (the "Exchange Act"), that are incorporated by
                  reference in this Registration Statement.

                        (b) That, for the purpose of determining any liability
                  under the Securities Act, each such post-effective amendment
                  shall be deemed to be a new registration statement relating to
                  the securities offered therein, and the offering of such
                  securities at that time shall be deemed to be the initial bona
                  fide offering thereof.

                        (c) To remove from registration by means of a
                  post-effective amendment any of the securities being
                  registered which remain unsold at the termination of the
                  offering.

      The Registrant hereby undertakes that, for purposes of determining any
liability under the Securities Act, each filing of the Registrant's annual
report pursuant to Section 13(a) or 15(d) of the Exchange Act (and, where
applicable, each filing of an employee benefit plan's annual report pursuant to
Section 15(d) of the Exchange Act) that is incorporated by reference in this
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered therein and the offering of such securities
at the time shall be deemed to be the initial bona fide offering thereof.

      Insofar as indemnification for liabilities arising under the Securities
Act of 1933 may be permitted to directors, officers and controlling persons of
the Registrant pursuant to the foregoing provisions, or otherwise, the
Registrant has been advised that in the opinion of the Securities and Exchange
Commission such indemnification is against public policy as expressed in the Act
and is, therefore, unenforceable. In the event that a claim for indemnification
against such liabilities (other than the payment by the Registrant of expenses
incurred or paid by a director, officer or controlling person of the Registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Act and will be governed by the final adjudication of
such issue.

      The Registrant hereby undertakes to file an application for the purpose of
determining the eligibility of the trustee to act under subsection (a) of
Section 310 of the Trust Indenture Act (the "Act") in accordance with the rules
and regulations prescribed by the Commission under Section 305(b)(2) of the Act.

                                      II-3


                                   SIGNATURES

      Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-3 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of The Woodlands, in the State of Texas, on January 21,
2005.

                                      LEXICON GENETICS INCORPORATED

                                      By: /s/ ARTHUR T. SANDS
                                          -------------------------------------
                                          Arthur T. Sands, M.D., Ph.D.
                                          President and Chief Executive Officer

                                POWER OF ATTORNEY

      Each person whose signature appears below appoints Arthur T. Sands and
Jeffrey L. Wade, and each of them, any of whom may act without the joinder of
the other, as his true and lawful attorneys-in-fact and agents with full power
of substitution and resubstitution, for him and in his name, place and stead, in
any and all capacities, to sign any and all amendments (including post-effective
amendments) to this Registration Statement and any Registration Statement
(including any amendment thereto) for this offering that is to be effective upon
filing pursuant to Rule 462(b) under the Securities Act of 1933, as amended, and
to file the same, with all exhibits thereto, and all other documents in
connection therewith, with the Securities and Exchange Commission, granting unto
said attorneys-in-fact and agents full power and authority to do and perform
each and every act and thing requisite and necessary to be done, as fully to all
intents and purposes as he might or would do in person, hereby ratifying and
confirming all that said attorneys-in-fact and agents or any of them or their or
his substitute and substitutes, may lawfully do or cause to be done by virtue
hereof.

      PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, AS AMENDED,
THIS REGISTRATION STATEMENT HAS BEEN SIGNED BELOW BY THE FOLLOWING PERSONS IN
THE CAPACITIES AND ON THE DATES INDICATED BELOW.



         SIGNATURE                                                       TITLE                                         DATE
------------------------------                      -----------------------------------------------               ----------------
                                                                                                            
                                                    President, Chief Executive Officer and Director               January 21, 2005
/s/ ARTHUR T. SANDS                                 (principal executive officer)
-----------------------------
Arthur T. Sands, M.D., Ph.D.

/s/ JULIA P. GREGORY                                Executive Vice President, Corporate Development               January 21, 2005
-----------------------------                        and Chief Financial Officer
Julia P. Gregory                                    (principal financial and accounting officer)

/s/ C. THOMAS CASKEY                                Chairman of the Board of Directors                            January 21, 2005
-----------------------------
C. Thomas Caskey, M.D.

/s/ SAM L. BARKER                                   Director                                                      January 21, 2005
-----------------------------
Sam L. Barker, Ph.D.

/s/ PATRICIA M. CLOHERTY                            Director                                                      January 21, 2005
-----------------------------
Patricia M. Cloherty

/s/ ROBERT J. LEFKOWITZ                             Director                                                      January 21, 2005
------------------------------
Robert J. Lefkowitz, M.D.

/s/ ALAN S. NIES                                    Director                                                      January 21, 2005
------------------------------
Alan S. Nies, M.D.

/s/ FRANK PALANTONI                                 Director                                                      January 21, 2005
-----------------------------
Frank Palantoni

/s/ CLAYTON S. ROSE                                 Director                                                      January 21, 2005
-----------------------------
Clayton S. Rose


                                      II-4



                                  EXHIBIT INDEX



 EXHIBIT NO.                                                    DESCRIPTION
-------------     ----------------------------------------------------------------------------------------------------------------
               
 *1.1      --     Form of Underwriting Agreement.
  3.1      --     Restated Certificate of Incorporation (filed as Exhibit 3.1 to the Company's Registration Statement on Form
                   S-1 (Registration No. 333-96469) and incorporated by reference herein).
  3.2      --     Restated Bylaws (filed as Exhibit 3.2 to the Company's Registration Statement on Form S-1
                   (Registration No. 333-96469) and incorporated by reference herein).
  4.1      --     Amended and Restated Registration Rights Agreement dated as of May 7, 1998 by and among the Company and the
                   stockholders named therein (filed as Exhibit 4.1 to the Company's Registration Statement on Form S-3
                   (Registration No. 333-67294) and incorporated by reference herein).
 *4.2      --     Form of Certificate of Designation of Preferred Stock.
  4.3      --     Form of Indenture.
 *4.4      --     Form of Note.
 *4.5      --     Form of Common Stock Warrant Agreement and Warrant Certificate.
 *4.6      --     Form of Preferred Stock Warrant Agreement and Warrant Certificate.
 *4.7      --     Form of Debt Securities Warrant Agreement and Warrant Certificate.
 *4.8      --     Form of Unit Agreement.
  5.1      --     Opinion of Vinson & Elkins L.L.P.
 12.1      --     Statement of Computation of Ratio of Earnings to Fixed Charges.
 23.1      --     Consent of Ernst & Young LLP.
 23.2      --     Consent of Vinson & Elkins L.L.P. (contained in Exhibit 5.1).
 24.1      --     Power of Attorney (contained in signature page).
*25.1      --     Statement of Eligibility of Trustee under the Indenture.


----------

*     To be filed by amendment, as an exhibit to a report filed under the
      Securities Exchange Act of 1934, as amended, or as otherwise required by
      regulation of the Securities and Exchange Commission, and incorporated by
      reference herein.