EXHIBIT 5.1

                                       
                                    May
                                    15th
                                    1 9 9 8



                                                                   003, 863-999
(213) 669-6000



Acacia Research Corporation
12 South Raymond Avenue
Pasadena, California  91105

          Re:  Registration Statement on Form S-3
               ----------------------------------

Ladies and Gentlemen:

          At your request, we have examined the Registration Statement on 
Form S-3 (the "Registration Statement") to be filed by you with the 
Securities and Exchange Commission on May 18, 1998 in connection with the 
registration under the Securities Act of 1933, as amended, of 634,786 shares 
of your Common Stock, no par value (the "Shares").

          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