As filed with the Securities and Exchange Commission on September 17, 2001.
                                                      Registration No. 333-61440
================================================================================
                      SECURITIES AND EXCHANGE COMMISSION
                             Washington, DC 20549

                              ___________________

                        POST-EFFECTIVE AMENDMENT NO. 1
                                      ON
                                   FORM S-8
                                      TO
                                   FORM S-4
                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933

                              ___________________

                         AMERISOURCEBERGEN CORPORATION
            (Exact name of Registrant as specified in its charter)

                                                                                  
                                             1300 Morris Drive, Suite 100
          Delaware                              Chesterbrook, PA 19087                      23-3079390
  (State of Incorporation)        (Address of principal executive offices) (Zip Code)    (I.R.S. Employer
                                                                                        Identification No.)


             AMERISOURCE HEALTH CORPORATION 2001 STOCK OPTION PLAN

       BERGEN BRUNSWIG CORPORATION 1999 MANAGEMENT STOCK INCENTIVE PLAN

                           (Full Title of the Plans)

                           William D. Sprague, Esq.
                         Vice President and Secretary
                         AmerisourceBergen Corporation
                         1300 Morris Drive, Suite 100
                            Chesterbrook, PA 19087
                    (Name and address of agent for service)
                                (610) 727-7000
         (Telephone number, including area code, of agent for service)

                                With a Copy to:

                            Craig L. Godshall, Esq.
                                    Dechert
                           4000 Bell Atlantic Tower
                               1717 Arch Street
                       Philadelphia, Pennsylvania  19103
                                (215) 994-4000




                                                  CALCULATION OF REGISTRATION FEE

-------------------------------------------------------------------------------------------------------------------------------
                                         Amount                   Proposed                Proposed               Amount Of
      Title Of Securities                To Be                Maximum Offering        Maximum Aggregate        Registration
        To Be Registered             Registered               Price Per Share          Offering Price               Fee
-------------------------------------------------------------------------------------------------------------------------------
                                                                                                
Common Stock of
 AmerisourceBergen Corporation,     4,240,654 shares (1)            N/A                      N/A                    (2)
 par value $.01 per share
-------------------------------------------------------------------------------------------------------------------------------


(1)  Represents 3,140,654 shares under the AmeriSource Health Corporation 2001
     Stock Option Plan and 1,100,000 shares under the Bergen Brunswig
     Corporation 1999 Management Stock Incentive Plan.

(2)  Not applicable. All filing fees payable in connection with the registration
     of the issuance of these securities were paid in connection with the filing
     of the Registrant's Form S-4 Registration Statement (333-61440) on May 23,
     2001.


This amendment shall become effective in accordance with the provisions of Rule
464 promulgated under the Securities Act of 1933.


                               EXPLANATORY NOTE

     AmerisourceBergen Corporation ("AmerisourceBergen" or the "Registrant")
hereby amends its Registration Statement on Form S-4 ("the Form S-4") by filing
this Post-Effective Amendment No. 1 on Form S-8 ("Post-Effective Amendment")
with respect to up to 4,240,654 shares of the Registrant's Common Stock, par
value $0.01 per share, issuable upon the exercise of stock options granted under
the AmeriSource Health Corporation 2001 Stock Option Plan and the Bergen
Brunswig Corporation 1999 Management Stock Incentive Plan (collectively, the
"Plans").

     Pursuant to an Agreement and Plan of Merger dated as of March 16, 2001,
AmeriSource Health Corporation ("AmeriSource"), a Delaware corporation, and
Bergen Brunswig Corporation ("Bergen"), a New Jersey corporation, jointly formed
the Registrant, a Delaware corporation, (formerly named AABB Corporation), with
two subsidiaries, A-Sub Acquisition Corp., a Delaware corporation, and B-Sub
Acquisition Corp., a New Jersey corporation. On August 29, 2001, A-Sub
Acquisition Corp. was merged with and into AmeriSource and B-Sub Acquisition
Corp. was merged with and into Bergen. As a result, AmeriSource and Bergen each
became a wholly-owned subsidiary of the Registrant. Pursuant to the Merger
Agreement, the Registrant assumed the obligations of AmeriSource and Bergen
under the Plans on the following terms:

     (i)  each option to purchase AmeriSource Common Stock (an "AmeriSource
Option") automatically was converted into an option to purchase shares of the
Registrant's Common Stock equal to the number of shares of AmeriSource Common
Stock issuable immediately prior to the effective time of the Merger upon
exercise of the AmeriSource Option, at an exercise price equal to the exercise
price of the AmeriSource option; and

     (ii) each option to purchase Bergen Common Stock (a "Bergen Option")
automatically was converted into an option to purchase shares of the
Registrant's Common Stock equal to the number of shares of Bergen Common Stock
issuable immediately prior to the effective time of the Merger upon exercise of
the Bergen Option multiplied by 0.37, at an exercise price equal to the exercise
price of the Bergen Option divided by 0.37.

     This designation of this Post-Effective Amendment as Registration No. 333-
61440 denotes that this Post-Effective Amendment relates only to the shares of
AmerisourceBergen Common Stock issuable upon the exercise of stock options under
the Plans and that this is the first Post-Effective Amendment on Form S-8 to the
Form S-4 filed with respect to such shares.

                                    PART II

              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.  Incorporation of Documents by Reference.

          The following documents of the Registrant, AmeriSource and Bergen
which have been filed with the Commission are incorporated by reference in this
Registration Statement as of their respective dates:


          (a)  AmeriSource's latest annual report on Form 10-K filed on December
20, 2000 for the year ended September 30, 2000;

          (b)  Bergen's latest annual report on Form 10-K filed on December 29,
2000 for the year ended September 30, 2000;

          (c)  all other reports filed by the Registrant, AmeriSource and Bergen
pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (the
"Exchange Act") since September 30, 2000;

          (d)  the description of the Registrant's Common Stock and the
Registrant's financial statements contained in the registration statement on
Form S-4 (File No. 333-61440), filed May 23, 2001, as amended, and including any
amendment or report filed for the purpose of updating such description;

          (e)  all documents subsequently filed by the Registrant with the
Commission pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act
after the date of this Registration Statement, but prior to the filing of a
post-effective amendment to this Registration Statement, which indicates that
all securities offered by this Registration Statement have been sold or which
deregisters all such securities then remaining unsold, shall be deemed to be
incorporated by reference into this Registration Statement. Each document
incorporated by reference into this Registration Statement shall be deemed to be
a part of this Registration Statement from the date of the filing of such
document with the Commission until the information contained therein is
superseded or updated by any subsequently filed document which is incorporated
by reference into this Registration Statement.


Item 4. Description of Securities.

          Not applicable.

Item 5. Interests of Named Experts and Counsel.

          Not Applicable.

Item 6. Indemnification of Directors and Officers.

          Delaware law provides that a corporation may include in its
certificate of incorporation a provision limiting or eliminating the liability
of its directors to the corporation and its stockholders for monetary damages
arising from a breach of fiduciary duty, except for:

  .  a breach of the duty of loyalty to the corporation or its stockholders;

  .  acts or omissions not in good faith or which involve intentional misconduct
     or a knowing violation of law;


  .  payment of a dividend or the repurchase or redemption of stock in violation
     of Delaware law; or

  .  any transaction from which the director derived an improper personal
     benefit.

     The amended and restated certificate of incorporation, as amended, of
AmerisourceBergen provides that the directors of AmerisourceBergen are entitled
to the benefits of all limitations on the liability of directors that are now or
hereafter become available under Delaware law.  Specifically, no director of
AmerisourceBergen will be liable to AmerisourceBergen or its stockholders for
monetary damages for breach of fiduciary duty as director, except for liability
(a) for any breach of the directors duty of loyalty to AmerisourceBergen or its
stockholders, (b) for acts or omissions not in good faith or which involve
intentional misconduct or a knowing violation of law, (c) under section 174 of
the Delaware law, which pertains, among other things, to liability for the
unlawful payment of dividends, or (d) for any transaction from which the
director derived an improper personal benefit.

     Under Delaware law, a corporation may indemnify directors and officers:

  .  for actions taken in good faith and in a manner they reasonably believed to
     be in, or not opposed to, the best interests of the corporation; and

  .  with respect to any criminal proceeding, if they had no reasonable cause to
     believe that their conduct was unlawful.

     In addition, Delaware law provides that a corporation may advance to a
director or officer expenses incurred in defending any action upon receipt of an
undertaking by the director or officer to repay the amount advanced if it is
ultimately determined that he or she is not entitled to indemnification.

     The amended and restated certificate of incorporation, as amended, of
AmerisourceBergen provides that AmerisourceBergen will indemnify any person who
is or was a director or officer of AmerisourceBergen, or is or was serving at
the request of AmerisourceBergen as a director, officer or trustee of another
corporation, trust or other enterprise, with respect to actions taken or omitted
by such person in any capacity in which such person serves AmerisourceBergen or
such other corporation, trust or other enterprise, to the full extent authorized
or permitted by law, as now or hereafter in effect, and such right to
indemnification will continue as to a person who has ceased to be a director,
officer or trustee, as the case may be, and will inure to the benefit of such
person's heirs, executors and personal and legal representatives.

Item 7. Exemption from Registration Claimed.

          Not applicable.


Item 8. Exhibits.

          The following exhibits are filed herewith or incorporated by reference
as part of this Registration Statement:

     Exhibit No.    Document
     -----------    --------

         3.1        Amended and Restated Certificate of Incorporation of the
                    Registrant (included as Annex J to the joint proxy
                    statement-prospectus forming a part of this Registration
                    Statement and incorporated herein by reference).

         3.2        Amended and Restated Bylaws of the Registrant (included as
                    Annex K to the joint proxy statement-prospectus forming a
                    part of this Registration Statement and incorporated herein
                    by reference).

         5.1        Opinion of Dechert (counsel to the Registrant).

        23.1        Consent of Ernst & Young LLP.

        23.2        Consent of Deloitte & Touche LLP.

        23.3        Consent of Dechert (included in Exhibit 5.1).

        24.1        Power of Attorney (included on signature page).

Item 9. Undertakings.

     (a)  The undersigned Registrant hereby undertakes:

          (1)  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;

               (ii) to reflect in the prospectus any facts or events arising
          after the effective date of the 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 the Registration Statement. Notwithstanding the foregoing, any
          increase or decrease in 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 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 the Registration
          Statement or any material change to such information in the
          Registration Statement;

provided, however, that paragraphs (a)(1)(i) and (a)(1)(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 with or furnished to the
Commission by the Registrant pursuant to Section 13 or 15(d) of the Exchange Act
that are incorporated by reference in the Registration Statement.

          (2)  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.

          (3)  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.

     (b)  The undersigned 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 the Registration Statement 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)  Insofar as indemnification for liabilities arising under the
Securities Act 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 Commission such
indemnification is against public policy as expressed in the Securities 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 Securities Act and will be governed by the final
adjudication of such issue.


                                  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-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Chesterbrook, Commonwealth of Pennsylvania, on
September 17, 2001.

                                                  AMERISOURCEBERGEN CORPORATION



                                                  By:      /s/ R. David Yost
                                                     ---------------------------
                                                  Name: R. David Yost
                                                  Title: President and Chief
                                                         Executive Officer

                               POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that each person whose signature appears
below constitutes and appoints R. David Yost as his attorney-in-fact and agent,
with full power of substitution and resubstitution, for him and in his name,
place, and stead, in any and all capacities, to sign and file this Registration
Statement and any and all pre- or post-effective amendments to such Registration
Statement, with all exhibits thereto and hereto, and other documents with the
Securities and Exchange Commission, granting unto said attorneys-in-fact and
agent, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as he might or could do in person, hereby
ratifying and confirming all that said attorneys-in-fact and agents, or any of
them, or their or his 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 by the following persons in the
capacities and on the dates indicated.

             Name                            Title                  Date


/s/ R. David Yost             President, Chief Executive     September 17, 2001
------------------------      Officer and Director
R. David Yost                 (Principal Executive Officer)



                                Executive Vice President and
/s/ Neil F. Dimick              Chief Financial Officer       September 17, 2001
------------------------------  (Principal Financial Officer
Neil F. Dimick                  and Principal Accounting
                                Officer)

/s/ Robert E. Martini           Chairman                      September 17, 2001
------------------------------
Robert E. Martini

/s/ James R. Mellor
------------------------------  Director                      September 17, 2001
James R. Mellor

/s/ Richard C. Gozon            Director                      September 17, 2001
------------------------------
Richard C. Gozon

/s/ Rodney H. Brady
------------------------------  Director                      September 17, 2001
Rodney H. Brady

/s/ Edward E. Hagenlocker       Director                      September 17, 2001
------------------------------
Edward E. Hagenlocker

/s/ Francis G. Rodgers          Director                      September 17, 2001
------------------------------
Francis G. Rodgers

/s/ J. Lawrence Wilson          Director                      September 17, 2001
------------------------------
J. Lawrence Wilson


                                 EXHIBIT INDEX
                                 -------------

Exhibit No.      Document
-----------      --------

     3.1         Amended and Restated Certificate of Incorporation of the
                 Registrant (included as Annex J to the joint proxy statement-
                 prospectus forming a part of this Registration Statement and
                 incorporated herein by reference).

     3.2         Amended and Restated Bylaws of the Registrant (included as
                 Annex K to the joint proxy statement-prospectus forming a part
                 of this Registration Statement and incorporated herein by
                 reference).

     5.1         Opinion of Dechert (counsel to the Registrant).

    23.1         Consent of Ernst & Young LLP.

    23.2         Consent of Deloitte & Touche LLP.

    23.3         Consent of Dechert (included in Exhibit 5.1).

    24.1         Power of Attorney (included on signature page).