Exhibit 99.1350CERT

         Certification Pursuant to Section 906 of the Sarbanes Oxley Act

I, Robert C. Doll, Jr., Chief Executive Officer of BlackRock Small Cap Index
Fund of BlackRock Index Funds, Inc. and Master Small Cap 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 Small Cap Index Fund of
                                               BlackRock Index Funds, Inc. and
                                               Master Small Cap 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 Small Cap Index Fund of
BlackRock Index Funds, Inc. and Master Small Cap Index Series of Quantitative
Master Series Trust and will be retained by BlackRock Small Cap Index Fund of
BlackRock Index Funds, Inc. and Master Small Cap 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 Small Cap Index Fund of
BlackRock Index Funds, Inc. and Master Small Cap 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 Small Cap Index Fund of
                                               BlackRock Index Funds, Inc. and
                                               Master Small Cap 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 Small Cap Index Fund of
BlackRock Index Funds, Inc. and Master Small Cap Index Series of Quantitative
Master Series Trust and will be retained by BlackRock Small Cap Index Fund of
BlackRock Index Funds, Inc. and Master Small Cap Index Series of Quantitative
Master Series Trust and furnished to the Securities and Exchange Commission or
its staff upon request.