Exhibit 5.1
Opinion of Counsel
                       BRENMAN BROMBERG & TENENBAUM, P.C.
                        1775 Sherman Street, Suite 1001
                             Denver, CO 80203-4314
                              Phone (303) 894-0234
                               Fax (303) 839-1633


                                  July 21, 1998

The Board of Directors
Entropin, Inc.
45926 Oasis Street
Indio, CA 92201

Re:      Form SB-2 Registration Statement
         Opinion of Counsel

Gentlemen:

         Reference  is  made  to the  registration  statement  (the"Registration
Statement")  on Form SB-2 filed by Entropin,  Inc. (the  "Company") on behalf of
certain shareholders of the Company ("Selling  Shareholders")  (Registration No.
333-51737)  filed  with  the  Securities  and  Exchange   Commission  under  the
Securities Act of 1933 , as amended. The Registration  Statement relates to: (i)
5,754,546  shares of Common Stock of the Company;  and,  (ii) 296,668  Shares of
Common Stock underlying options.

         We have  acted  as  counsel  to the  Company  in  connection  with  the
preparation of the  Registration  Statement  relating to the proposed  resale of
shares of Common Stock by the Selling  Shareholders.  In such capacity,  we have
examined the  originals or copies,  certified  or otherwise  identified,  of the
Articles of Incorporation,  as restated and amended,  and Bylaws, as amended, of
the Company,  corporate  records of the Company,  including  minute books of the
Company as furnished to us by the Company,  certificates of public officials and
of representatives of the Company,  statutes and other records,  instruments and
documents  pertaining  to the  Company as a basis for the  opinions  hereinafter
expressed. In giving such opinions, we have relied upon certificates of officers
of the Company with respect to the accuracy of the factual matters  contained in
such certificates.

         Based upon the  foregoing and subject to the other  qualifications  and
limitations stated in this letter, we are of the opinion that:

         (1)      The Company is a  corporation  duly  incorporated  and validly
                  existing  in good  standing  under  the  laws of the  State of
                  Colorado; and

         (2)      The  shares  of  Common  Stock  to  be  sold  by  the  Selling
                  Shareholders have been duly authorized and are validly issued,
                  fully paid and non-assessable.

         (3)      The  shares of Common  Stock to be  issued to  holders  of the
                  options  and  the  Selling  Shareholders,  upon  exercise  and
                  payment of the exercise price stated in the options




Entropin, Inc.
July 21, 1998
Page 2
                  held  by  the  Selling  Shareholders,   will  have  been  duly
                  authorized, validly issued, fully paid and non-assessable.

         This  opinion  is a legal  opinion  and not an opinion as to matters of
fact.  This  opinion  is limited  to the laws of the State of  Colorado  and the
federal law of the United States of America,  and to the matters  stated herein.
This  opinion  is made as of the date  hereof,  and  after the date  hereof,  we
undertake  no, and disclaim  any,  obligation to advise you of any change in any
matters  set forth  herein,  and we  express  no opinion as to the effect of any
subsequent  course of dealing or conduct  between the  parties.  This opinion is
furnished to you solely in connection with the transactions  referred to herein,
and may not be  relied  on,  quoted  by or  otherwise  referred  to by any other
person, firm or entity without our prior written consent.

         We hereby consent to the filing of this opinion with the Securities and
Exchange  Commission  as an exhibit  to the  Registration  Statement  and to the
reference to our firm under "Legal Matters" in the Prospectus.

                                        Very truly yours,


                                        /s/ Brenman Bromberg & Tenenbaum, P.C.