10-K EXHIBIT 24 POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS THAT the undersigned directors and officers of McKesson Corporation, 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, under the Securities Act of 1934, as amended, an Annual Report on Form 10-K for the fiscal year ended March 31, 2003, and thereafter to execute and file any and all amendments to such Form, whether filed prior or subsequent to the time such Form 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/ Tully M. Friedman /s/ Robert W. Matschullat - ----------------------------------------- ----------------------------------- Tully M. Friedman, Director Robert W. Matschullat, Director /s/ William R. Graber /s/ James V. Napier - ----------------------------------------- ----------------------------------- William R. Graber, Senior Vice President James V. Napier, Director and Chief Financial Officer (Principal Financial Officer) /s/ John H. Hammergren /s/ Carl E. Reichardt - ----------------------------------------- ----------------------------------- John H. Hammergren, Chairman, President, Carl E. Reichardt, Director Chief Executive Officer and Director (Principal Executive Officer) /s/ Alton F. Irby III /s/ Jane E. Shaw - ----------------------------------------- ----------------------------------- Alton F. Irby III, Director Jane E. Shaw, Director /s/ M. Christine Jacobs /s/ Richard F. Syron - ----------------------------------------- ----------------------------------- M. Christine Jacobs, Director Richard F. Syron, Director /s/ Marie L. Knowles /s/ Nigel A. Rees - ----------------------------------------- ----------------------------------- Marie L. Knowles, Director Nigel A. Rees, Vice President and Controller (Principal Accounting Officer) Dated: March 26, 2003