Exhibit 99.1350CERT

         Certification Pursuant to Section 906 of the Sarbanes Oxley Act

      I, Terry K. Glenn, President of Merrill Lynch Small Cap Index Fund and
      Master Small Cap Index Series (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: February 23, 2004


                                                /s/ Terry K. Glenn
                                                ------------------
                                                Terry K. Glenn,
                                                President of
                                                Merrill Lynch Small Cap Index
                                                Fund and Master Small Cap Index
                                                Series

      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 Small Cap Index Fund and Master Small Cap Index Series and will be
      retained by Merrill Lynch Small Cap Index Fund and Master Small Cap Index
      Series 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 Small Cap
      Index Fund and Master Small Cap Index Series (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: February 23, 2004


                                                /s/ Donald C. Burke
                                                -------------------
                                                Donald C. Burke,
                                                Chief Financial Officer of
                                                Merrill Lynch Small Cap Index
                                                Fund and Master Small Cap Index
                                                Series

      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 Small Cap Index Fund and Master Small Cap Index Series and will be
      retained by Merrill Lynch Small Cap Index Fund and Master Small Cap Index
      Series and furnished to the Securities and Exchange Commission or its
      staff upon request.