EXHIBIT 24.2
                               POWER OF ATTORNEY

     Each of the undersigned directors and each of the undersigned officers of
McKesson HBOC, Inc., a Delaware corporation (the "Corporation"), does hereby
constitute and appoint Ivan D. Meyerson and Kristina Vesco as his or her true
and lawful attorney-in-fact and agent, each with full power of substitution and
resubstitution, for him or her and in his or her name, place and stead in any
and all capacities, to execute and deliver in his or her name and on his or her
behalf:

     (a) One or more Registration Statements (with all exhibits thereto) of the
Corporation on Form S-3 or any other appropriate form proposed to be filed by
the Corporation with the Securities and Exchange Commission (the "SEC")
(including, without limitation, Registration Statements filed pursuant to Rule
462 under the Securities Act of 1933, as amended, or any successor thereto (the
"Securities Act")) for the purpose of registering under the Securities Act,
shares of the Corporation's common stock, par value $0.01 (the "Shares"), that
were issued in connection with the merger of Automated Prescription Systems with
and into the Corporation;

     (b) any and all supplements and amendments (including, without limitation,
post-effective amendments) to such Registration Statements; and

     (c) any and all other documents and instruments in connection with the
registration of the Shares which such attorney-in-fact and agent deems necessary
or advisable to enable the Corporation to comply with (i) the Securities Act,
the Securities Exchange Act of 1934, as amended, and the other federal
securities laws of the United States of America and the rules, regulations and
requirements of the SEC in respect of any thereof; (ii) the securities or Blue
Sky laws of any state or other governmental subdivision of the United States of
America; and (iii) the securities or similar applicable laws of any foreign
jurisdiction,

and each of the undersigned hereby grants unto such attorney-in-fact or his
substitute or substitutes, each and every act and thing requisite and necessary
to be done in and about the premises as fully as to all intents and purposes as
he or she might or could do in person, and does hereby ratify and confirm as his
or her own acts deeds all that such attorney-in-fact and agent, or his
substitute or substitutes, shall lawfully do or cause to be done by virtue
hereof. Such attorney-in-fact and agent shall have, and may exercise, all of the
powers hereby conferred.

     IN WITNESS WHEREOF, the undersigned has hereunto subscribed this power of
attorney this 6th day of August, 1999.



        /s/ John H. Hammergren                        /s/ David L. Mahoney
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        John H. Hammergren                            David L. Mahoney