EXHIBIT 5.1

                               OPINION OF COUNSEL

August 8, 2002

Mercury Interactive Corporation
1325 Borregas Avenue
Sunnyvale, California 94089

     Re: Registration Statement on Form S-8
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Ladies and Gentlemen:

     We have examined the Registration Statement on Form S-8 to be filed by you
with the Securities and Exchange Commission on or about August 9, 2002 (the
"Registration Statement") in connection with the registration under the
Securities Act of 1933, as amended, of a total of 500,000 shares of your Common
Stock (the "Shares") reserved for issuance under the 1998 Employee Stock
Purchase Plan (the "Plan"). As legal counsel for Mercury Interactive
Corporation, we have examined the proceedings taken and are familiar with the
proceedings proposed to be taken by you in connection with the sale and issuance
of the Shares under the Plan.

     It is our opinion that, when issued and sold in the manner referred to in
the Plan and pursuant to the agreement which accompanies each grant under the
Plan, the Shares will be legally and validly issued, fully paid and
nonassessable.

     We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to the use of our name wherever it appears in the
Registration Statement and any amendments thereto.

                                            Very truly yours,

                                            GENERAL COUNSEL ASSOCIATES LLP

                                            /s/ General Counsel Associates LLP