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                                                                     EXHIBIT 5.1

                         [GUNDERSON DETTMER LETTERHEAD]

                               November 15, 1999

Quintus Corporation
47212 Mission Falls Court
Fremont, California 94539

     Re:  Registration Statement on Form S-1

Ladies and Gentlemen:

     We have examined the Registration Statement on Form S-1 originally filed by
Quintus Corporation (the "Company") with the Securities and Exchange Commission
(the "Commission") on November 15, 1999, pursuant to Rule 462(b) under the
Securities Act, as thereafter amended or supplemented (the "Registration
Statement"), in connection with the registration under the Securities Act of
1933, as amended, of up to 575,000 shares of the Company's Common Stock (the
"Shares"). The Shares, which include an over-allotment option granted by the
Company to the Underwriters to purchase up to 75,000 additional shares of the
Company's Common Stock, are to be sold to the Underwriters by the Company as
described in the Registration Statement for resale to the public. As your
counsel in connection with this transaction, 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.

     It is our opinion that, upon completion of the proceedings being taken or
contemplated by us, as your counsel, to be taken prior to the issuance of the
Shares being sold by the Company and upon completion of the proceedings being
taken in order to permit such transactions to be carried out in accordance
with the securities laws  of the various states where required, the Shares
being sold by the Company, when issued and sold in the manner described in the
Registration Statement and in accordance with the resolutions adopted by the
Board of Directors of the Company, will be legally and validly issued, fully
paid and non-assessable.

     We consent to the use of this opinion as an exhibit to said Registration
Statement and further consent to the use of our name wherever appearing in said
Registration Statement, including the prospectus constituting a part thereof,
and in any amendment or supplement thereto.

                                       Very truly yours,

                                       /s/ Gunderson Dettmer Stough
                                           Villeneuve Franklin & Hachigian, LLP
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