EXHIBIT 5.1
                             September 19, 1996



Thermatrix Inc.
101 Metro Drive, Suite 248
San Jose, CA 95110

     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 September 20, 1996 (the
"Registration Statement") in connection with the registration under the
Securities Act of 1933, as amended, of an aggregate of 1,280,332 shares of
your Common Stock, par value $0.001 per share (the "Shares"), (i) 746,997
shares of which are currently outstanding under the 1987 Stock Plan, 
(ii) 333,334 shares of which are issuable pursuant to the 1996 Stock Plan, 
(iii) 83,334 shares of which are issuable pursuant to the 1996 Director Option
Plan and (iv) 116,667 shares of which are issuable pursuant to the Employee
Stock Purchase Plan (collectively, the "Plans"). 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
issuance and sale of the Shares pursuant to the Plans.

     It is our opinion that, when issued and sold in the manner described in the
Plans and pursuant to the agreements which accompany each grant under the Plans,
the Shares will be legally and validly issued, fully-paid and non-assessable.

     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 appearing in the
Registration Statement and any amendments thereto.

                              Very truly yours,

                              WILSON SONSINI GOODRICH & ROSATI


                              \s\ WILSON SONSINI GOODRICH & ROSATI