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                                    EXHIBIT 5


                                  June 22, 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 5,000,000 shares of the Company's Common stock, and options to
purchase shares of the Company's Common stock, par value $0.01 per share,
issuable pursuant to the McKesson HBOC, Inc. 1999 Stock Option and Restricted
Stock Plan (the "1999 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 1999 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