EXHIBIT 23.4
 
MORGAN STANLEY DEAN WITTER
 
                                                                  1585 BROADWAY
                                                       NEW YORK, NEW YORK 10036
                                                                 (212) 761-4000
                                                            
                                                         November 27, 1998     
 
Board of Directors
HBO & Company
301 Perimeter Center North
Atlanta, GA 30346
 
Dear Sirs:
   
  We hereby consent to the inclusion in the Registration Statement of McKesson
Corporation ("McKesson") on Form S-4, with respect to the shares of common
stock, par value $0.01 per share of McKesson, of our opinion letter appearing
as Annex E to the Joint Proxy Statement/Prospectus which is part of the
Registration Statement and to the references of our firm name therein. In
giving such consent, we do not thereby admit that we come within the category
of persons whose consent is required under Section 7 of the Securities Act of
1933, as amended, or the rules and regulations adopted by the Securities and
Exchange Commission thereunder, nor do we admit that we are experts with
respect to any part of the Registration Statement within the meaning of the
term "experts" as used in the Securities Act of 1933, as amended, or the rules
and regulations of the Securities and Exchange Commission thereunder.     
 
                                     Very truly yours,
 
                                     MORGAN STANLEY & CO. INCORPORATED
 
                                     By: /s/ Mary Anne Citrino
                                       ---------------------------------------
 
                                             Mary Anne Citrino
                                             Managing Director