Exhibit 99.1350CERT

         Certification Pursuant to Section 906 of the Sarbanes Oxley Act

      I, Terry K. Glenn, President of Merrill Lynch Global Balanced Fund of
      Mercury Funds, Inc. and Merrill Lynch Master Global Balanced Portfolio of
      Mercury Master 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: July 19, 2004


                                        /s/ Terry K. Glenn
                                        ------------------
                                        Terry K. Glenn,
                                        President of
                                        Merrill Lynch Global Balanced Fund of
                                        Mercury Funds, Inc. and Merrill Lynch
                                        Master Global Balanced Portfolio of
                                        Mercury Master 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 Global Balanced Fund of Mercury Funds, Inc. and Merrill Lynch Master
      Global Balanced Portfolio of Mercury Master Trust and will be retained by
      Merrill Lynch Global Balanced Fund of Mercury Funds, Inc. and Merrill
      Lynch Master Global Balanced Portfolio of Mercury Master Trust and
      furnished to the Securities and Exchange Commission or its staff upon
      request.



Exhibit 99.1350CERT

         Certification Pursuant to Section 906 of the Sarbanes Oxley Act

      I, Donald C. Burke, Chief Financial Officer of Merrill Lynch Global
      Balanced Fund of Mercury Funds, Inc. and Merrill Lynch Master Global
      Balanced Portfolio of Mercury Master 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: July 19, 2004


                                        /s/ Donald C. Burke
                                        -------------------
                                        Donald C. Burke,
                                        Chief Financial Officer of
                                        Merrill Lynch Global Balanced Fund of
                                        Mercury Funds, Inc. and Merrill Lynch
                                        Master Global Balanced Portfolio of
                                        Mercury Master 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 Global Balanced Fund of Mercury Funds, Inc. and Merrill Lynch Master
      Global Balanced Portfolio of Mercury Master Trust and will be retained by
      Merrill Lynch Global Balanced Fund of Mercury Funds, Inc. and Merrill
      Lynch Master Global Balanced Portfolio of Mercury Master Trust and
      furnished to the Securities and Exchange Commission or its staff upon
      request.