August 7, 1998 Via Telecopier (415) 983-8826 McKesson Corporation One Post Street San Francisco, CA 94104 Attention: Ivan D. Meyerson, Esq. Reference is hereby made to that certain Agreement and Plan of Merger by and among McKesson Corporation,...

                          [AmeriSource Letterhead]

                               August 7, 1998

Via Telecopier (000) 000-0000

McKesson Corporation
Xxx Xxxx Xxxxxx
Xxx Xxxxxxxxx, XX  00000
Attention:  Xxxx X. Xxxxxxxx, Esq.

          Reference is hereby made to that certain Agreement and Plan of
Merger by and among McKesson Corporation, Patriot Acquisition Corp. and
AmeriSource Health Corporation ("AmeriSource"), as amended (the "Merger
Agreement"). Capitalized terms used in this letter that are not otherwise
defined shall have the meanings ascribed to them in the Merger Agreement.

          We are hereby notifying you that AmeriSource hereby exercises its
right to terminate the Merger Agreement pursuant to Section 7.1(c) of the
Merger Agreement.

                                    Very truly yours,

                                    AMERISOURCE HEALTH CORPORATION


                                    By:  /s/ Xxxxxx Xxxxx Xxxx
                                       ------------------------------
                                        Name:
                                        Title:


cc:   Xxxxx, Xxxxx, Xxxxxx, Xxxxxxx & Xxxxxxxx
      Xxx Xxx Xxxx Xxxxx
      Xxx Xxxx, Xxx Xxxx  00000
      Attention:  Xxxxxxx Xxxxxxx, P.C.

      XXXXX XXXXXXXX, ESQ. (VIA TELECOPIER)