Exhibit 99.1350CERT

         Certification Pursuant to Section 906 of the Sarbanes Oxley Act

I, Robert C. Doll, Jr., Chief Executive Officer of BlackRock S&P 500 Index Fund
of BlackRock Index Funds, Inc. and Master S&P 500 Index Series of Quantitative
Master Series 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: February 20, 2007


                                                /s/ Robert C. Doll, Jr.
                                                --------------------------------
                                                Robert C. Doll, Jr.,
                                                Chief Executive Officer of
                                                BlackRock S&P 500 Index Fund of
                                                BlackRock Index Funds, Inc. and
                                                Master S&P 500 Index Series of
                                                Quantitative Master Series 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 BlackRock S&P 500 Index Fund of
BlackRock Index Funds, Inc. and Master S&P 500 Index Series of Quantitative
Master Series Trust and will be retained by BlackRock S&P 500 Index Fund of
BlackRock Index Funds, Inc. and Master S&P 500 Index Series of Quantitative
Master Series 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 BlackRock S&P 500 Index Fund of
BlackRock Index Funds, Inc. and Master S&P 500 Index Series of Quantitative
Master Series 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: February 20, 2007


                                                /s/ Donald C. Burke
                                                --------------------------------
                                                Donald C. Burke,
                                                Chief Financial Officer of
                                                BlackRock S&P 500 Index Fund of
                                                BlackRock Index Funds, Inc. and
                                                Master S&P 500 Index Series of
                                                Quantitative Master Series 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 BlackRock S&P 500 Index Fund of
BlackRock Index Funds, Inc. and Master S&P 500 Index Series of Quantitative
Master Series Trust and will be retained by BlackRock S&P 500 Index Fund of
BlackRock Index Funds, Inc. and Master S&P 500 Index Series of Quantitative
Master Series Trust and furnished to the Securities and Exchange Commission or
its staff upon request.