1
                                                                     EXHIBIT 5.1


                          OPINION OF BUCHANAN INGERSOLL

                                February 23, 2001


Demegen, Inc.
1051 Brinton Road
Pittsburgh, PA  15221

Ladies and Gentlemen:

         We have acted as counsel to Demegen, Inc., a Colorado corporation (the
"Company"), in connection with the preparation and filing of the Registration
Statement on Form SB-2 (the "Registration Statement") of the Company, under the
Securities Act of 1933, as amended, relating to the intended resale from time to
time by certain security holders (in the manner described in the prospectus (the
"Prospectus") contained in the Registration Statement) of up to an aggregate of
16,251,314 shares of the Company's common stock, par value $0.001 per share (the
"Shares"), of which (a) 5,642,879 Shares are currently outstanding; and (b) up
to 10,608,435 Shares are issuable upon the exercise of certain currently
outstanding warrants. We have examined such corporate records, other documents,
and questions of law as we have considered necessary or appropriate for the
purposes of this opinion.

         We express no opinion as to the applicability or compliance with or
effect of federal law or the law of any other jurisdiction other than the
Colorado Business Corporation Act, as amended.

         Based on the foregoing, we are of the opinion that, the Shares have
been legally issued, fully paid and nonassessable.

         We consent to the filing of this opinion as an exhibit to the
Registration Statement and the reference to this firm under the caption
"Interest of Named Experts and Counsel - Legal Matters" in the Prospectus
contained therein.



                                       Very truly yours,

                                       BUCHANAN INGERSOLL
                                       PROFESSIONAL CORPORATION



                                       By: /s/ Mary L. Silverberg
                                          --------------------------------
                                                Mary L. Silverberg