(As filed on September 25, 2003)
                                                               File No. 70-10078


                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D. C. 20549
                    ________________________________________

                                     POS AMC

                         POST-EFFECTIVE AMENDMENT NO. 1
                                (Amendment No. 4)
                                       to
                                    FORM U-1
                           APPLICATION OR DECLARATION
                                    UNDER THE
                   PUBLIC UTILITY HOLDING COMPANY ACT OF 1935
                     ______________________________________

                               AMEREN CORPORATION
                              1901 Chouteau Avenue
                            St. Louis, Missouri 63103

                                  CILCORP INC.
                       CILCORP INVESTMENT MANAGEMENT INC.
                              CILCORP VENTURES INC.
                    AMERENENERGY RESOURCES GENERATING COMPANY
                               300 Liberty Street
                             Peoria, Illinois 61602

                  (Names of companies filing this statement and
                    addresses of principal executive offices)
                     _______________________________________

                               AMEREN CORPORATION

                 (Name of top registered holding company parent)
                      _____________________________________





                               Steven R. Sullivan
                        Vice President Regulatory Policy,
                          General Counsel and Secretary
                             Ameren Services Company
                              1901 Chouteau Avenue
                            St. Louis, Missouri 63103

                     (Name and address of agent for service)
                ________________________________________________
                  The Commission is requested to send copies of
                 all notices, orders and other communications in
                connection with this Application/Declaration to:

      Ronal K. Evans,                        William T. Baker, Jr., Esq.
      Managing Associate General Counsel     Thelen Reid & Priest LLP
      Ameren Services Company                875 Third Avenue
      1901 Chouteau Avenue                   New York, New York  10022
      St. Louis, Missouri 63103


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ITEM 1. DESCRIPTION OF PROPOSED TRANSACTION.
        -----------------------------------

     1.1 Background. Ameren Corporation ("Ameren"), whose principal business
address is at 1901 Chouteau Avenue, St. Louis, Missouri 63103, is a registered
holding company under the Public Utility Holding Company Act of 1935, as amended
(the "Act"). Ameren directly owns all of the issued and outstanding common stock
of Union Electric Company d/b/a AmerenUE ("AmerenUE") and Central Illinois
Public Service Company d/b/a AmerenCIPS ("AmerenCIPS"), and indirectly through
CILCORP Inc. ("CILCORP"), an exempt holding company, owns all of the issued and
outstanding common stock of Central Illinois Light Company, d/b/a AmerenCILCO
("AmerenCILCO"). Together, AmerenUE, AmerenCIPS and AmerenCILCO provide retail
and wholesale electric service to approximately 1.7 million customers and retail
natural gas service to approximately 500,000 customers in parts of Missouri and
Illinois. In addition, AmerenCILCO holds all of the outstanding common stock of
AmerenEnergy Resources Generating Company (f/k/a Central Illinois Generation,
Inc.) ("AERG"). AERG is currently an "exempt wholesale generator" ("EWG") under
Section 32 of the Act, but will relinquish such status and become an additional
public-utility subsidiary of Ameren upon the transfer of substantially all of
AmerenCILCO's generation assets to AERG. Such transfer is currently expected to
take place in the fourth quarter of 2003. Ameren, CILCORP and AERG are sometimes
referred to herein collectively as the "Applicants."

     By order dated January 29, 2003, in this proceeding (Holding Co. Act
Release No. 27645) (the "Prior Order"), the Commission authorized Ameren to
acquire all of the issued and outstanding common stock of CILCORP. Ameren
completed its acquisition of CILCORP on January 31, 2003. In the Prior Order,
the Commission also authorized CILCORP, AmerenCILCO and AERG to engage in a
program of external long-term and short term financing and intrasystem financing
transactions for the period through March 31, 2006, subject to various
conditions and limitations and to a reservation of jurisdiction over the
investment grade criteria applicable to long-term debt securities of CILCORP and
AERG. The Commission also reserved jurisdiction under the Prior Order over
Ameren's retention of certain indirect non-utility subsidiaries and investments
of CILCORP, as described below.

     The Applicants are filing this post-effective amendment (i) to request a
release of jurisdiction over the investment grade criteria applicable to
CILCORP's and AERG's long-term debt securities, (ii) to acknowledge that certain
indirect non-utility subsidiaries and investments of CILCORP, as described
below, are not retainable under the standards of the Act and, in connection
therewith, to request that the Commission enter an order pursuant to Section
11(b)(1) of the Act directing Ameren to sell or otherwise dispose of the stock
or assets of such subsidiaries, and (ii) to request findings by the Commission
that certain other indirect investments held by CILCORP, also as described
below, are retainable under the standards of the Act, subject to a condition.

     1.2 Modification of Investment Grade Criteria. Among other specific
approvals granted by the Prior Order, the Commission authorized (1) CILCORP to
issue and sell in one or more transactions unsecured long-term notes
("Refinancing Notes") for the purpose of refinancing or acquiring certain
outstanding senior notes of CILCORP in an aggregate amount equal to the unpaid


                                       3



principal amount of such outstanding senior notes plus any "make whole" premium
required to be paid in connection with any prepayment and/or premium paid in
connection with any acquisition of such senior notes on the open market, and (2)
AERG to issue from time to time any combination of preferred stock, other
preferred securities and long-term debt securities ("Long-term Securities") in
an aggregate amount not to exceed $500 million at any time outstanding.

     Among other terms and conditions applicable to the Refinancing Notes and
the Long-term Securities, the Prior Order states:

     Except in accordance with a further order of the Commission in this
     proceeding, CILCORP and [AERG] will not publicly issue any Refinancing
     Notes [ . . . ] or Long-term Securities [ . . . ], respectively,
     unless the securities are rated at the investment grade level as
     established by at least one nationally recognized statistical rating
     organization, as that term is used in paragraphs (c)(2)(vi)(E), (F)
     and (H) of Rule 15c3-1 under the Securities Exchange Act of 1934.
     CILCORP and [AERG] request that the Commission reserve jurisdiction
     over the investment grade criteria with respect to the undertaking in
     the previous sentence and commit to file a post-effective amendment in
     this proceeding on or before September 30, 2003 to seek authorization
     to use such investment grade criteria.

     In accordance with the aforementioned reservation of jurisdiction under the
Prior Order, CILCORP and AERG are now requesting authorization to continue to
use the investment grade criteria quoted above after September 30, 2003, with
certain modifications to reflect the Commission's current policy on investment
grade criteria as applied to securities issued by registered holding companies
and their subsidiaries./1/ Specifically, CILCORP and AERG represent that:

     No Refinancing Notes or Long-term Securities will be issued by CILCORP
     or AERG, respectively, in reliance upon the authorization granted by
     the Commission under the Prior Order, unless (i) the security to be
     issued, if rated, is rated investment grade; (ii) all outstanding
     securities of the issuer that are rated are rated investment grade;
     and (iii) all outstanding securities of the top level registered
     holding company that are rated are rated investment grade. For
     purposes of this provision, a security will be deemed to be rated
     "investment grade" if it is rated investment grade by at least one
     nationally recognized statistical rating organization ("NRSRO"), as
     that term is used in paragraphs (c)(2)(vi)(E), (F) and (H) of Rule
     15c3-1 under the Securities Exchange Act of 1934, as amended. CILCORP
     and AERG request that the Commission reserve jurisdiction over the
     issuance of any such securities that are rated below investment grade.
     CILCORP and AERG further request that the Commission reserve
     jurisdiction over the issuance of any guarantee or other securities at
     any time that the conditions set forth in clauses (i) through (iii)
     above are not satisfied.

----------
1    See SCANA Corporation, Holding Company Act Release No. 27649 (Feb. 12,
     2003).


                                       4



     1.3 Non-Retainable and Retainable Interests of CILCORP. Under the Prior
Order, the Commission reserved jurisdiction over Ameren's retention of the
following direct and indirect subsidiaries and investments of CILCORP Investment
Management, Inc. ("CIM") and CILCORP Ventures Inc. ("CVI"), each of which is a
direct wholly-owned subsidiary of CILCORP:

          (a)  Subsidiaries of CIM.
               -------------------

          CIM Leasing Inc. ("CIM Leasing"), a direct subsidiary of CIM, owns,
among other investments, passenger railcars that are leased to a foreign
governmental entity pursuant to a leveraged lease.

          CIM Air Leasing Inc. ("Air Leasing"), also a direct subsidiary of CIM,
holds a 40% partnership interest in Freighter Express Partners, which leases a
commercial aircraft to Federal Express.

          CILCORP Lease Management Inc. ("CLM"), also a direct subsidiary of
CIM, holds investments in several leveraged lease transactions. CLM directly
holds a 7% interest as an owner participant in an owner-trust that leases Unit
No. 1 of the Springerville Power Plant to Tucson Electric Power Company. In
addition, CLM has the following wholly-owned subsidiaries which own passive
interests in leveraged leases: CLM Inc., IV is a general partner and a limited
partner in D.C.L. Leasing Partners Limited Partnership, Ltd. - IV, which leases
an office building in California to Xerox Corporation;/2/ CLM X, Inc., through
two wholly-owned subsidiaries (CLM XI, Inc. and CLM Inc., VI) holds general and
limited partnership interests in D.C.L. Leasing Partners Limited Partnership,
Ltd. - VI, which leases an office building in Delaware to Hercules, Inc. and
through CLM Inc., VI also owns an undivided interest in a waste-to-energy
electric generating facility with AVI-TWENTE, B.V., which is majority-owned by a
number of municipalities in the Netherlands; and CLM Inc. - VII and CLM Inc.
VIII each owns a 50% undivided interest in 24 separate commercial real estate
properties located in eight states that are leased to Walmart for use in its
Sam's Wholesale Clubs operations.

     At December 31, 2002, CIM's aggregate net investment in the above leveraged
leases was approximately $26 million.

          (b)  Subsidiaries and Investments of CVI.
               -----------------------------------

          Agricultural Research and Development Corporation ("ARDC"), an
80%-owned subsidiary of CVI,/3/ serves as the conduit for investments in
ventures formed to commercialization agricultural research in central Illinois
as part of a combined private/government effort to boost the local economy and

----------
2    In connection with the upcoming refinancing of the partnership's
     indebtedness, it is anticipated that CLM will be required to separate its
     general and partnership interests into two separate entities.

3    CVI holds 80% of the common stock of ARDC; EDC, Inc., the Economic
     Development Council for the Peoria Area, holds the remaining 20%.


                                       5


create jobs in the region. ARDC funds these investments through Biotechnology
Research and Development Corporation ("BRDC"). BRDC provides research grants to
universities and other research organizations. ARDC currently owns about 11% of
the common stock of BRDC. At December 31, 2002, CVI's investment in ARDC was
approximately $38,000.

          Other Investments. CVI holds a 2% membership interest in Peoria Chiefs
Community Baseball Club, L.L.C. ("Peoria Chiefs"), which owns a minor league
baseball team, and 4.2% of the outstanding common stock of Peoria Medical
Research Corporation ("PMRC"), the general partner of a limited partnership
engaged in clinical research. At December 31, 2002, CVI's investment in these
entities was approximately $225,000.

     Under the Prior Order, the Commission directed Ameren to file a
post-effective amendment in this proceeding on or before January 31, 2004 to
request authorization to the above-described subsidiaries and investments of CIM
and CVI or, alternatively, commit to divest them as non-retainable interests
under the Act.

     Section 11(b)(1) provides that the Commission "may permit as reasonably
incidental, or economically necessary or appropriate to the operations" of a
registered holding company system "the retention of an interest in any business
.. . . which the Commission shall find necessary or appropriate in the public
interest or for the protection of investors or consumers and not detrimental to
the proper functioning" of such holding company system. The Commission has
traditionally interpreted this provision as requiring an operating or functional
relationship between the non-utility activity and the holding company's core
utility business./4/ Section 11(b)(1), by its terms, was not applicable to
CILCORP prior to its acquisition by Ameren. Under Section 9(c)(3) of the Act,
the Commission has also authorized registered holding companies and their
subsidiaries to make or retain passive investments (i.e., investments that do
not result in the creation of an "affiliate" relationship) "in the ordinary
course of business." This provision has been interpreted to permit, among other
things, the acquisition or retention of passive investments in low-income
housing projects qualifying for tax credits/5/ and other types of local economic
development activities./6/ In one case, the Commission authorized a registered
holding company to make passive equity investments in leveraged leases for the
purpose of obtaining tax benefits in the form of accelerated depreciation and
investment credits./7/

     Ameren has concluded that the leveraged lease investments of CIM and CVI's
membership interest in Peoria Chiefs are not retainable under the standards of
either Section 9(c)(3) or Section 11(b)(1) of the Act. With regard to Section
11(b)(1), there is no operating or functional relationship between any of these
investments and Ameren's core utility operations. In addition, with regard to
Section 9(c)(3), certain of the leveraged lease investments held by CIM are not

----------
4    See Michigan Consolidated Gas Co., 44 S.E.C. 361 (1970), affd. Michigan
     Consolidated Gas Company v. SEC, 444 F.2d 913 (1970).

5    See e.g., the Prior Order.

6    See e.g., Ameren Corporation, Holding Co. Act Release No. 26809 (Dec. 30,
     1997).

7    Central and South West Corporation, et al., 49 S.E.C. 323 (1985).


                                       6



passive, since CIM is a general as well as a limited partner. Further, CIM has
already captured substantially all of the tax benefits (in the form of
accelerated depreciation) available under these leases. Likewise, CVI's
investment in Peoria Chiefs is not sufficiently linked to local economic
development activity in Ameren's service territory./8/ Accordingly, Ameren will
undertake to sell or otherwise dispose of (i) all of the stock of CIM Leasing,
Air Leasing and CLM and/or the assets (including, without limitation,
partnership interests) held by such companies in the leveraged leases described
above, and (ii) CVI's membership interest in Peoria Chiefs (such stock, other
interests and assets collectively referred to hereafter as the "Non-Retainable
Interests"), in one or more transactions, to one or more purchasers.

     If the Commission concurs with Ameren's conclusion that such companies and
investments are not retainable, then it is requested that the order of the
Commission in this proceeding: (i) recite that such sale or disposition is
necessary or appropriate to the integration or simplification of the Ameren
holding company system and to effectuate the provisions of Section 11(b)(1);
(ii) require Ameren to take the appropriate actions to cause CIM and CVI and/or
any subsidiary or either company, as the case may be, to complete the sale or
disposition of the Non-Retainable Interests not later than January 31, 2006;
(iii) require that the net proceeds from such sale or disposition be utilized
within 24 months of the receipt thereof to retire or cancel securities
representing indebtedness of the transferor or otherwise expended for property
other than "nonexempt property" within the meaning of section 1083 of the
Internal Revenue Code, as amended (the "Code") or invested as a contribution to
the capital, or as paid-in surplus, of another direct or indirect subsidiary of
Ameren in a manner that satisfies the nonrecognition provisions of Code section
1081; and (iv) recite that such expenditure or investment by the transferor is
necessary or appropriate to the integration or simplification of the Ameren
holding company system. This is intended to enable Ameren to obtain the tax
treatment for any gain on such sale or disposition provided for in section 1081
of the Code./9/

----------
8    See CP&L Energy, Inc., Holding Co. Act Release No. 27284 (Nov. 27, 2000)
     (finding limited partnership interest in Tampa Bay Devil Rays, Ltd., the
     owner of a major league baseball franchise, to be non-retainable under the
     standards of the Act).

9    Section 1081(f) of the Code specifies that in order for section 1081 to
     apply to an exchange, investment, distribution or sale, the order of the
     Commission in obedience to which such transaction was made must recite that
     such transaction is necessary or appropriate to effectuate the provisions
     of Section 11(b) of the Act and specifies and itemizes the stock and
     securities and other property which are ordered to be acquired,
     transferred, received or sold. Section 1081(b)(2) of the Code further
     specifies that if property received in connection with any sale or
     disposition is "nonexempt property" (which is defined to include cash),
     then such nonexempt property must, within 24 months of the time of the
     transfer, in accordance with an order of the Commission, be expended for
     other property other than nonexempt property (which, under section
     1081(b)(3), would include retirement of the transferor's indebtedness) or
     invested as a contribution to the capital, or as paid-in surplus, of
     another corporation, and the Commission's order must recite that such
     expenditure or investment by the transferor corporation is necessary or
     appropriate to the integration or simplification of the holding company
     system of which the transferor corporation is a member.


                                       7



     Ameren believes that CVI's 4.2% interest in PMRC is retainable under the
standards of Section 9(c)(3) of the Act. The Commission has previously permitted
new registered holding companies to retain passive and/or de minimis investments
in ventures formed to promote local economic development through, among other
things, investment in research and development of new technologies./10/ ARDC's
interest in BRDC would be retainable under these same precedents if ARDC owned
less than 5% of the voting securities of BRDC. Accordingly, Ameren commits to
reduce ARDC's ownership interest in the voting securities of BRDC to below 5% of
the total number outstanding on or before January 31, 2006 either by selling
some or all of such shares or by converting voting securities of BRDC into
non-voting securities.

ITEM 2. FEES, COMMISSIONS AND EXPENSES.
        ------------------------------

     The additional fees, commissions and expenses paid or incurred and to be
paid or incurred in connection with the proposals contained herein are estimated
not to exceed $8,000.

ITEM 3. APPLICABLE STATUTORY PROVISIONS.
        -------------------------------

     Sections 6(a), 7, 9(c)(3) and 11(b)(1) of the Act are applicable to the
proposed transactions. The proposed transactions are also subject to Rule 54.
Rule 54 provides that, in determining whether to approve the issue or sale of
any securities for purposes other than the acquisition of an EWG or "foreign
utility company" ("FUCO") or other transactions unrelated to EWGs or FUCOs, the
Commission shall not consider the effect of the capitalization or earnings of
subsidiaries of a registered holding company that are EWGs or FUCOs if Rule
53(a), (b) and (c) are satisfied. Under Rule 53(a), the Commission shall not
make certain specified findings under Sections 7 and 12 in connection with a
proposal by a holding company to issue securities for the purpose of acquiring
the securities of or other interest in an EWG, or to guarantee the securities of
an EWG, if each of the conditions in paragraphs (a)(1) through (a)(4) thereof
are met, provided that none of the conditions specified in paragraphs (b)(1)
through (b)(3) of Rule 53 exists. These standards are met.

     Rule 53(a)(1): Ameren's "aggregate investment" (as defined in Rule
53(a)(1)) in EWGs as of June 30,2003 was $470,655,404, or approximately 26.5% of
Ameren's "consolidated retained earnings" (also as defined in Rule 53(a)(1)) for
the four quarters ended June 30, 2003 ($1,773,093,901). Ameren does not
currently hold an interest in any FUCO.

     Rule 53(a)(2): Ameren will maintain books and records enabling it to
identify investments in and earnings from each EWG and FUCO in which it directly
or indirectly acquires and holds an interest. Ameren will cause each domestic
EWG in which it acquires and holds an interest, and each foreign EWG and FUCO
that is a majority-owned subsidiary, to maintain its books and records and

----------
10   Ameren Corporation, supra n. 6 (citing cases in footnote 12 of Appendix A).
     Also see Rule 40(a)(5)(ii), which exempts from Section 9(a) any acquisition
     of securities issued by local industrial or other nonutility enterprises
     located in the acquiring company's service territory, subject to annual
     aggregate investment limit of $1 million, provided that no affiliate
     relationship is established.


                                       8



prepare its financial statements in conformity with U.S. generally accepted
accounting principles. All of such books and records and financial statements
will be made available to the Commission, in English, upon request.

     Rule 53(a)(3): No more than 2% of the employees of Ameren's domestic
utility subsidiaries will, at any one time, directly or indirectly, render
services to EWGs and FUCOs.

     Rule 53(a)(4): Ameren will submit a copy of each Application/Declaration
relating to investments in EWGs and FUCOs and copies of any related Rule 24
certificates, as well as a copy of Ameren's Form U5S, to each of the public
service commissions having jurisdiction over the retail rates of Ameren's
domestic utility subsidiaries.

     In addition, Ameren states that the provisions of Rule 53(a) are not made
inapplicable to the authorization herein requested by reason of the occurrence
or continuance of any of the circumstances specified in Rule 53(b). Rule 53(c)
is inapplicable by its terms.

ITEM 4. REGULATORY APPROVAL.
        -------------------

     The proposed transaction is not subject to the jurisdiction of any state
commission or of any federal commission other than this Commission.

ITEM 5. PROCEDURE.
        ---------

     The Applicants request that the Commission issue a supplemental order in
this proceeding soon as practicable and in any event not later than September
30, 2003. The Applicants further request that there be no thirty-day waiting
period between the issuance of the Commission's order and the date on which it
is to become effective. The Applicants hereby waive a recommended decision by a
hearing officer or other responsible officer of the Commission and consent to
the participation of the Division of Investment Management in the preparation of
the Commission's decision and/or order in the proceeding unless such Division
opposes the matters covered hereby.

ITEM 6. EXHIBITS AND FINANCIAL STATEMENTS.
        ---------------------------------

        a. Exhibits.
           --------

                (no additional exhibits are filed herewith)

        b. Financial Statements.
           --------------------

           FS-1  -  Ameren Consolidated Balance Sheet as of December 31, 2002,
                    and Consolidated Statement of Income and Consolidated
                    Statement of Cash Flows for the year ended December 31, 2002
                    (Incorporated by Reference to Ameren's Annual Report on Form
                    10-K for the period year ended December 31, 2002) (File No.
                    1-14756).


                                       9



           FS-2  -  Ameren Consolidated Balance Sheet as of June 30, 2003, and
                    Consolidated Statement of Income and Consolidated Statement
                    of Cash Flows for the six months ended June 30, 2003
                    (Incorporated by Reference to Ameren's Quarterly Report on
                    Form 10-Q for the period ended June 30, 2003) (File No.
                    1-14756).

ITEM 7. INFORMATION AS TO ENVIRONMENTAL EFFECTS.
        ---------------------------------------

     The Commission's action in this matter will not constitute a major federal
action significantly affecting the quality of the human environment. No other
federal agency has prepared or is preparing an environmental impact statement
with regard to the proposed transactions.

                                   SIGNATURES

     Pursuant to the requirements of the Public Utility Holding Company Act of
1935, as amended, the undersigned companies have duly caused this Post-Effective
Amendment to be signed on their behalves by the undersigned thereunto duly
authorized.

                                         AMEREN CORPORATION
                                         CILCORP INC.
                                         CILCORP INVESTMENT MANAGEMENT
                                           INC.
                                         CILCORP VENTURES INC.
                                         AMERENENERGY RESOURCES
                                           GENERATING COMPANY

                                         By: /s/ Steven R. Sullivan
                                                 ------------------
                                         Name:  Steven R. Sullivan
                                         Title: Vice President, General Counsel,
                                                and Secretary


Date: September 25, 2003


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