Exhibit 32.1 CERTIFICATE OF THE PRINCIPAL EXECUTIVE OFFICER OF DIOMED HOLDINGS, INC. (REGISTRANT) PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002 I, James A. Wylie, Jr., Chief Executive Officer of the Registrant, certify to the best of my knowledge and belief pursuant to Section 906 of Sarbanes-Oxley Act of 2002 (18 U.S.C. Section 1350) that: (1) The Quarterly Report on Form 10-QSB for the period ended June 30, 2003, which this statement accompanies, 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 Quarterly Report on Form 10-QSB fairly presents, in all material respects, the financial condition and result of operations of the Registrant. Date: August 14, 2003 /s/ JAMES A. WYLIE, JR. --------------------------- James A. Wylie, Jr. Chief Executive Officer (Principal Executive Officer) 18