Exhibit 32.1

         Certification Pursuant to Section 906 of the Sarbanes Oxley Act


I, Terry K. Glenn, President of Merrill Lynch Funds for Institutions Series and
Master Institutional Money Market Trust (together, the "Fund"), certify that:

      1.    The N-CSR of the Fund (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 Fund.


Dated: June 18, 2004


                                       /s/ Terry K. Glenn
                                       -------------------------
                                       Terry K. Glenn,
                                       President of
                                       Merrill Lynch Funds for Institutions
                                       Series and Master Institutional
                                       Money Market Trust


A signed original of this written statement required by Section 906, or other
document authenticating, acknowledging, or otherwise adopting the signature that
appears in typed form within the electronic version of this written statement
required by Section 906, has been provided to Merrill Lynch Funds for
Institutions Series and Master Institutional Money Market Trust and will be
retained by Merrill Lynch Funds for Institutions Series and Master Institutional
Money Market Trust and furnished to the Securities and Exchange Commission or
its staff upon request.