<Page>

                       State Street Research Institutional Funds
                                  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, the undersigned
officer of the State Street Research Institutional Funds, a Massachusetts
business trust, (the "Trust"), does hereby certify that the Trust's report on
Form N-CSR for the period ended July 31, 2003 (the "N-CSR") fully complies
with the requirements of Section 13 (a) or 15 (d), as applicable, of the
Securities Exchange Act of 1934, as amended, and information contained in the
N-CSR fairly presents, in all material respects, the financial condition and
the results of operations of the Trust. This certification is provided solely
pursuant to 18 U.S.C. 1350 and shall not be deemed a part of the N-CSR, the
financial statements filed with the N-CSR or otherwise "filed" for any
purpose.

Date: September 29, 2003


                                 /s/ Douglas A. Romich
                                 Douglas A. Romich
                                 Treasurer

<Page>

                       State Street Research Institutional Funds
                                  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, the undersigned
officer of the State Street Research Institutional Funds, a Massachusetts
business trust, (the "Trust"), does hereby certify that the Trust's report on
Form N-CSR for the period ended July 31, 2003 (the "N-CSR") fully complies
with the requirements of Section 13 (a) or 15 (d), as applicable, of the
Securities Exchange Act of 1934, as amended, and information contained in the
N-CSR fairly presents, in all material respects, the financial condition and
the results of operations of the Trust. This certification is provided solely
pursuant to 18 U.S.C. 1350 and shall not be deemed a part of the N-CSR, the
financial statements filed with the N-CSR or otherwise "filed" for any
purpose.

Date: September 29, 2003


                                 /s/ Richard S. Davis
                                 Richard S. Davis
                                 President, Chairman and Chief Executive Officer