NxStage Medical 10-Q 2007 Q2 Quarterly report

EXHIBIT 32.2

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 of NxStage Medical, Inc. (the “Company”) for the period ended June 30, 2007 as filed with the Securities and Exchange Commission on the date hereof (this “report”), I, Robert S. Brown, Chief Financial Officer of the Company, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that, to my knowledge:

(1)	This 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 this report fairly presents, in all material respects, the financial condition and results of operations of the Company.

	/s/ Robert S. Brown
	Robert S. Brown
	Chief Financial Officer
	(principal financial and accounting officer)
Date: August 9, 2007

A signed original of this written statement required by Section 906 of the Sarbanes-Oxley Act of 2002 has been provided to the Company and will be retained by the Company and furnished to the Securities and Exchange Commission or its staff upon request