EXHIBIT 24 POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS THAT the undersigned directors and officers of McKesson Corporation, (formerly McKesson HBOC, Inc.) a Delaware corporation (the "Company") do hereby constitute and appoint Ivan D. Meyerson and Kristina Veaco his or her true and lawful attorney and agent, each with full power and authority (acting alone and without the other) to execute in the name and on behalf of the undersigned as such Director and/or Officer, a Registration Statement on Form S-8 under the Securities Act of 1933, as amended, with respect to the registration of shares of the Company's Common Stock, par value $.01 per share, that may be issued by the Company under the McKesson Corporation (formerly McKesson HBOC, Inc.) Profit-Sharing Investment Plan, and to execute any and all amendments to such Registration Statement, whether filed prior or subsequent to the time such Registration Statement becomes effective. The undersigned hereby grants unto such attorneys and agents, and each of them, full power of substitution and revocation in the premises and hereby ratifies and confirms all that such attorneys and agents may do or cause to be done by virtue of these presents. /s/Alfred C. Eckert III /s/Martin M. Koffel Director Director /s/Tully M. Friedman /s/Gerald E. Mayo Director Director /s/William R. Graber /s/James V. Napier Senior Vice President and Chief Director Financial Officer /s/John H. Hammergren, /s/Carl E. Reichardt President and Director Chief Executive Officer and Director /s/Alton F. Irby, III /s/Alan Seelenfreund Director Chairman of the Board and Director /s/Jane E. Shaw Director Dated: March 21, 2002 EXHIBIT 24 POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS THAT the undersigned Officer of McKesson Corporation (formerly McKesson HBOC, Inc.), a Delaware corporation (the "Company") does hereby constitute and appoint Ivan D. Meyerson and Kristina Veaco his true and lawful attorney and agent, each with full power and authority (acting alone and without the other) to execute in the name and on behalf of the undersigned as such Officer, a Registration Statement on Form S-8 under the Securities Act of 1933, as amended, with respect to the registration of shares and plan interests of the Company's Common Stock, par value $.01 per share, that may be issued by the Company under the McKesson Corporation (formerly McKesson HBOC, Inc.) Profit-Sharing Investment Plan, and to execute any and all amendments to such Registration Statement, whether filed prior or subsequent to the time such Registration Statement becomes effective. The undersigned hereby grants unto such attorneys and agents, and each of them, full power of substitution and revocation in the premises and hereby ratifies and confirms all that such attorneys and agents may do or cause to be done by virtue of these presents. /s/ Nigel A. Rees Nigel A. Rees Vice President and Controller Dated: March 21, 2002