EXHIBIT 5 February 10, 2000 McKesson HBOC, Inc. McKesson Plaza One Post Street San Francisco, CA 94104 I am Senior Vice President, General Counsel and Secretary of McKesson HBOC, Inc., a Delaware corporation (the "Company"). In that capacity I have reviewed the Registration Statement on Form S-8 to be filed by the Company with the Securities and Exchange Commission under the Securities Act of 1933 with respect to 500,000 shares of the Company's Common stock, par value $0.01 per share, issuable pursuant to the 1998 Canadian Stock Incentive Plan. As General Counsel, I am familiar with the Company's Restated Certificate of Incorporation and its Restated By-Laws, as amended to date. I have also examined such other documents, corporate records and instruments as I have deemed necessary or appropriate for the purpose of this opinion. Based upon the foregoing, I am of the opinion that the shares of Common Stock of the Company, when issued in accordance with the Canadian Stock Incentive Plan, will be legally issued, fully paid and nonassessable. I hereby consent to the filing of this opinion with the Securities and Exchange Commission as Exhibit 5 to the Registration Statement. Very truly yours, /s/Ivan D. Meyerson Ivan D. Meyerson Senior Vice President, General Counsel and Corporate Secretary