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February 25, 2002




Morgan Stanley S&P 500 Index Fund
Harborside Financial Center, Plaza Two
Jersey City, New Jersey 07311

Ladies and Gentlemen:

         This opinion is being furnished to Morgan Stanley S&P 500 Index Fund,
a Massachusetts business trust (the "Trust"), in connection with the
Registration Statement on Form N-14 (the "Registration Statement") under the
Securities Act of 1933, as amended (the "1933 Act"), to be filed by the Trust
in connection with the acquisition by the Trust of substantially all of the
assets of Morgan Stanley S&P 500 Select Fund ("500 Select"), in exchange for
shares of beneficial interest of the Trust (the "Shares"), and the assumption
by the Trust of certain stated liabilities of 500 Select pursuant to an
Agreement and Plan of Reorganization dated as of January 24, 2002 between the
Trust and 500 Select (the "Reorganization Agreement"). We have examined such
statutes, regulations, corporate records and other documents and reviewed such
questions of law as we deemed necessary or appropriate for the purposes of
this opinion.

         As to matters of Pennsylvania law contained in this opinion, we have
relied upon the opinion of Nutter, McClennen & Fish, LLP, dated February 25,
2002.

         Based upon the foregoing, we are of the opinion that the Trust Shares
when issued, as described in the Reorganization Agreement, will be duly and
validly authorized and, assuming receipt of the consideration to be paid
therefor, upon delivery as provided in the Reorganization Agreement, will be
legally issued, fully paid and non-assessable (except for the potential
liability of shareholders described in the Trust's Statement of Additional
Information dated October 31, 2001 under the caption "Capital Stock And Other
Securities").

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to us in the Prospectus forming a
part of the Registration Statement. We do not thereby admit that we are within
the category of persons whose consent is







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MAYER, BROWN, ROWE & MAW
Page 2



required under Section 7 of the 1933 Act or the rules and regulations of the
Securities and Exchange Commission thereunder.


                               Very truly yours,



                               /s/ Mayer, Brown, Rowe & Maw