FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person * HAMMERGREN JOHN H   2. Issuer Name and Ticker or Trading Symbol MCKESSON CORP [MCK] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) Chairman, President & CEO (Last) (First) (Middle) ONE POST STREET 3. Date of Earliest Transaction (Month/Day/Year) 05/22/2010 (Street) SAN FRANCISCO, CA 94104 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 05/22/2010   M   94,050 A $ 0 581,229.925 I By Trust (1) Common Stock 05/22/2010   F   42,440 (2) D $ 68.33 538,789.925 I By Trust (3) Common Stock               3,988.6066 I By Profit-Sharing Investment Plan

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Restricted Stock Units

$ 0

05/22/2010

M

94,050

(4)

(4)

Common Stock

94,050

$ 0

0

D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
HAMMERGREN JOHN H ONE POST STREET SAN FRANCISCO, CA 94104	X		Chairman, President & CEO

Signatures

Donna Spinola, Attorney-in-fact		05/25/2010
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Represents 281,617.925 shares held under the Hammergren Family Trust; 11,174 shares held under the JHH 2008 GRAT; 11,174 shares held under the WLH 2008 GRAT; 82,479 shares held under the JHH GRAT No. 4; 82,479 shares held under the WLH GRAT No. 4; 14,038 shares held under the JHH GRAT No. 5; 14,038 shares held under the WLH GRAT No. 5; 14,038 shares held under the JHH GRAT No. 6; 14,038 shares held under the WLH GRAT No. 6; 14,038 shares held under the JHH GRAT No. 7; 14,038 shares held under the WLH GRAT No. 7; 14,039 shares held under the JHH GRAT No. 8; 14,039 shares held under the WLH GRAT No. 8
(2)	This transaction represents a withholding of shares to cover taxes applicable to a vesting of RSUs also reported on this Form 4.
(3)	Represents 239,177.925 shares held under the Hammergren Family Trust; 11,174 shares held under the JHH 2008 GRAT; 11,174 shares held under the WLH 2008 GRAT; 82,479 shares held under the JHH GRAT No. 4; 82,479 shares held under the WLH GRAT No. 4; 14,038 shares held under the JHH GRAT No. 5; 14,038 shares held under the WLH GRAT No. 5; 14,038 shares held under the JHH GRAT No. 6; 14,038 shares held under the WLH GRAT No. 6; 14,038 shares held under the JHH GRAT No. 7; 14,038 shares held under the WLH GRAT No. 7; 14,039 shares held under the JHH GRAT No. 8; 14,039 shares held under the WLH GRAT No. 8
(4)	These units were granted on 5/22/2007 and vested as follows: 50% on 5/22/2008 and 50% on 5/22/2010.

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