Charles River Laboratories International (CRL) 10-Q 2007 Q2 Quarterly report

Exhibit 32.1

CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,
AS ADOPTED PURSUANT TO
SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the quarterly report on Form 10-Q for the period ended June 30, 2007 of Charles River Laboratories International, Inc. (the “Company”) as filed with the Securities and Exchange Commission on the date hereof (the “Report”), the undersigned, James C. Foster, the Chairman, Chief Executive Officer and President, and Thomas F. Ackerman, Corporate Executive Vice President and Chief Financial Officer, each hereby certifies, to the best of his knowledge and pursuant to 18 U.S.C. Section 1350, that:

(1)the Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2)the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Dated: August 8, 2007	/s/ JAMES C. FOSTER
	James C. Foster
	Chairman, President and Chief Executive Officer
	Charles River Laboratories International, Inc.
Dated: August 8, 2007	/s/ THOMAS F. ACKERMAN
	Thomas F. Ackerman
	Corporate Executive Vice President & Chief Financial Officer
	Charles River Laboratories International, Inc.

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