Certification
                Pursuant to Section 906 of the Sarbanes-Oxley Act
                of 2002 (Subsections (a) and (b) of Section 1350,
                  Chapter 63 of Title 18, United States Code)

         Pursuant to section 906 of the Sarbanes-Oxley Act of 2002 (subsections
(a) and (b) of section 1350, chapter 63 of title 18, United States Code), the
undersigned officer of Instinet Group Incorporated, a Delaware corporation (the
"Company"), does hereby certify, to the best of such officer's knowledge, that:

         The Quarterly Report on Form 10-Q for the quarter ended June 30, 2002
(the "Form 10-Q") of the Company fully complies with the requirements of section
13(a) or 15(d) of the Securities Exchange Act of 1934 and information contained
in the Form 10-Q fairly presents, in all material respects, the financial
condition and results of operations of the Company.

Dated:   August 13, 2002                   /s/ Mark Nienstedt
                                           ------------------------------------
                                           Mark Nienstedt
                                           Acting President and Chief Executive
                                           Officer, and Chief Financial Officer


         The foregoing certification is being furnished solely pursuant to
section 906 of the Sarbanes-Oxley Act of 2002 (subsections (a) and (b) of
section 1350, chapter 63 of title 18, United States Code) and is not being filed
as part of the Form 10-Q or as a separate disclosure document.