EXHIBIT 5.1

August 26, 1998



Acacia Research Corporation
12 South Raymond Avenue
Pasadena, California 91105


             RE: REGISTRATION STATEMENT ON FORM S-8

Ladies and Gentlemen:

     At your request, we have examined the Registration Statement on Form S-8 
(the "Registration Statement") to be filed by you with the Securities and 
Exchange Commission on August 26, 1998 in connection with the registration 
under the Securities Act of 1933, as amended, of 500,000 shares of your 
Common Stock, no par value (the "Shares") for your 1996 Stock Option Plan (as 
amended).

     We are familiar with the proceedings heretofore taken, and with the 
additional proceedings proposed to be taken, by you in connection with the 
authorization and proposed issuance and sale of the Shares.

     It is our opinion that, subject to said proceedings being duly taken and 
completed by you prior to the issuance and sale of the Shares, upon the 
issuance and sale thereof in the manner referred to in the Registration 
Statement, 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.


                                                 Respectfully submitted,


                                                 /s/ O'Melveny & Myers LLP