<PAGE>

                       SECURITIES AND EXCHANGE COMMISSION

                              Washington, DC 20549

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

                                    FORM 8-K

                                 CURRENT REPORT

     PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

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

       Date of Report (Date of earliest event reported): December 13, 2002

                          AmerisourceBergen Corporation
             (Exact name of Registrant as specified in its charter)


<TABLE>
<S>                                             <C>                                         <C>
               Delaware                                 1-16671                                 23-3079390
(State or Other Jurisdiction of                 Commission File Number                       (I.R.S. Employer
Incorporation or Organization)                                                                Identification
                                                                                                  Number)
</TABLE>



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


                          1300 Morris Drive, Suite 100
                      Chesterbrook, Pennsylvania 19087-5594
   (Address, Including Zip Code, and Telephone Number, Including Area Code, of
                    Registrant's Principal Executive Offices)

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

                                      n/a
           (Former name or former address, if changed since last report)

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


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Item 5.  Other Events.
         ------------

         On December 13, 2002, AmerisourceBergen Corporation (the "Company")
announced the signing of a definitive agreement to purchase US Bioservices
Corporation, a national pharmaceutical service provider focused on the
management of high-cost, complex therapies and reimbursement support. The
transaction has a base purchase price valued at approximately $160,000,000
(including assumed debt) and provides for contingency payments of up to a
maximum of $30 million, both the base purchase price and the contingency
payments being subject to certain potential adjustments at closing. The Company
has agreed to issue approximately 2.4 million shares of its common stock upon
the closing of the transaction.

         A copy of the press release is filed as Exhibit 99.1 to this report and
incorporated herein by reference.



Item 7.  Financial Statements and Exhibits.
          --------------------------------

         (c)      Exhibits.
                  99.1     Press Release dated December 13, 2002


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                                   SIGNATURES
                                   ----------

         Pursuant to the requirements of the Securities Exchange Act of 1934,
the Registrant has duly caused this report to be signed on its behalf
by the undersigned hereunto duly authorized.


                                    AMERISOURCEBERGEN CORPORATION

Date: December 13, 2002             By:    /s/  Michael D. DiCandilo
                                    ---------------------------------------
                                          Name:  Michael D. DiCandilo
                                          Title:  Senior Vice President and
                                                  Chief Financial Officer




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                                                                    Exhibit 99.1

                                                                    News Release

                                                   AmerisourceBergen Corporation
                                                   P.O. Box 959
                                                   Valley Forge, PA 19482

[LOGO OF AMERISOURCEBERGEN]

Contact:    Michael N. Kilpatric
            610-727-7118
            mkilpatric@amerisource.com

                      AMERISOURCEBERGEN SIGNS AGREEMENT TO
                      PURCHASE US BIOSERVICES CORPORATION

   Largest Pharmaceutical Distributor Adds Specialty Pharmaceuticals Services
                                    Business

         VALLEY FORGE, Pa. December 13, 2002--AmerisourceBergen Corporation
(NYSE:ABC), the largest pharmaceutical services company in the U.S. dedicated
solely to the pharmaceutical supply channel, today announced that it has signed
a definitive agreement to purchase US Bioservices Corporation, a privately held
company (approximately 58 percent of which is owned by Whitney and Company), in
a transaction with a base purchase price valued at approximately $160 million
including assumed debt. The agreement also provides for contingent payments of
up to $30 million based on US Bioservices achieving defined earnings targets
through the end of the first quarter of calendar year 2004. Both the base
purchase price and the contingent payments are subject to potential adjustments
at closing. The transaction is expected to close during the March 2003 quarter.

US Bioservices is a national pharmaceutical services provider focused on the
management of high-cost, complex therapies and reimbursement support, and it
anticipates revenues of about $120 million in the 2002 calendar year.

         AmerisourceBergen expects the acquisition to be slightly accretive to
the Company's fiscal 2003 earnings per share expectations of 20 percent growth
over the previous year's 42 percent earnings per share increase, excluding
special charges.

         "We look forward to the contribution that US Bioservices will make to
our specialty pharmaceutical business," said R. David Yost, AmerisourceBergen's
Chief Executive Officer. "US Bioservices brings service capabilities in a
variety of areas including special pediatrics therapies, complex blood therapies
and reimbursement services."

         "Adding US Bioservices expands the Company's capability to support the
unique needs that pharmaceutical manufacturers have when they launch complex
products into the small, targeted markets that are important to many
biotechnology pharmaceutical companies," said Steven H. Collis, Senior Vice
President and President of AmerisourceBergen Specialty Group. "Manufacturers can
come to AmerisourceBergen for complete support in launching new specialty
products, including distribution and logistics, physician and patient education,
and reimbursement."

         AmerisourceBergen has agreed to issue approximately 2.4 million shares
of its common stock upon the closing of the transaction. The shares of common
stock that AmerisourceBergen has agreed to issue upon the closing of the
transaction have not been registered under the Securities Act of 1933 and may
not be offered or sold in the United States absent registration or an applicable
exemption from registration requirements. This news release shall not constitute
an offer to sell or a solicitation of an offer to buy such shares in any
jurisdiction in which such an offer or sale would be unlawful.


<PAGE>

                                                                    News Release

About AmerisourceBergen

AmerisourceBergen (NYSE:ABC) is the largest pharmaceutical services company in
the United States dedicated solely to the pharmaceutical supply chain. It is the
leading distributor of pharmaceutical products and services to the hospital
systems/acute care market, alternate care and mail order facilities, independent
community pharmacies, and regional chain pharmacies. The Company is also a
leader in the institutional pharmacy marketplace. With more than $40 billion in
annualized operating revenue, AmerisourceBergen is headquartered in Valley
Forge, PA, and employs more than 13,000 people serving over 25,000 customers.
For more information got to www.amerisourcebergen.com.

Forward-Looking Statements

This news release may contain certain "forward-looking statements" within the
meaning of Section 27A of the Securities Act of 1933 and Section 21E of the
Securities Exchange Act of 1934. These statements are based on management's
current expectations and are subject to uncertainty and changes in
circumstances. Actual results may vary materially from the expectations
contained in the forward-looking statements. Forward-looking statements may
include statements addressing future financial and operating results of
AmerisourceBergen and the benefits and aspects of the 2001 merger between
AmeriSource Health Corporation and Bergen Brunswig Corporation.


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                                                                    News Release

The following factors, among others, could cause actual results to differ
materially from those described in the forward-looking statements: the risk that
the businesses of AmeriSource and Bergen Brunswig will not be integrated
successfully; failure to obtain and retain expected synergies; and other
economic, business, competitive and/or regulatory factors affecting the business
of AmerisourceBergen generally.

More detailed information about these factors is set forth in
AmerisourceBergen's filings with the Securities and Exchange Commission,
including its Annual Report on Form 10-K for fiscal 2001, its Quarterly Reports
on Form 10-Q for fiscal 2002, and the joint proxy statement-prospectus for the
merger filed on August 1, 2001.

AmerisourceBergen is under no obligation to (and expressly disclaims any such
obligation to) update or alter any forward-looking statements whether as a
result of new information, future events or otherwise.