EXHIBIT 99.1

                            CERTIFICATION PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

     In connection with the Quarterly Report of AmerisourceBergen Corporation
(the "Company") on Form 10-Q for the fiscal quarter ended March 31, 2003 as
filed with the Securities and Exchange Commission on the date hereof (the
"Report"), I, R. David Yost, Chief Executive Officer of the Company, certify,
pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the
Sarbanes-Oxley Act of 2002, that to the best of my knowledge:

         (1) The Report fully complies with the requirements of Section 13(a) or
15(d) of the Securities Exchange Act of 1934; and

         (2) The information contained in the Report fairly presents, in all
material respects, the financial condition and results of operations of the
Company.

/s/  R. DAVID YOST
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     R. David Yost
     Chief Executive Officer
     May 12, 2003