Exhibit 5.1

                          [LATHAM & WATKINS LETTERHEAD]

                                                                  March 29, 2002

Aderis Pharmaceuticals, Inc.
85 Main Street
Hopkinton, Massachusetts 01748


     Re: Registration Statement No. 333-76612; 6,325,000 shares of
         Common Stock, par value $0.001 per share
         ----------------------------------------

Ladies and Gentlemen:

     In connection with the registration of 6,325,000 shares of common stock of
the Company, par value $0.001 per share (the "Shares"), under the Securities Act
of 1933, as amended (the "Act"), by Aderis Pharmaceuticals, Inc., a Delaware
corporation (the "Company"), on Form S-1 filed with the Securities and Exchange
Commission (the "Commission") on January 11, 2002 (File No. 333-76612), as
amended by Amendment No. 1 filed with the Commission on March 29, 2002, as it
may be further amended (collectively, the "Registration Statement"), you have
requested our opinion with respect to the matters set forth below.

     In our capacity as your special counsel in connection with such
registration, we are familiar with the proceedings taken and proposed to be
taken by the Company in connection with the authorization, issuance, and sale of
the Shares, and for the purposes of this opinion, have assumed such proceedings
will be timely completed in the manner presently proposed. In addition, we have
made such legal and factual examinations and inquiries, including an examination
of originals or copies certified or otherwise identified to our satisfaction of
such documents, corporate records and instruments, as we have deemed necessary
or appropriate for the purposes of this opinion.

     In such examination, we have assumed the genuineness of all signatures, the
authenticity of all documents submitted to us as originals, and the conformity
to authentic original documents of all documents submitted to us as copies.

     We are opining herein as to the effect on the subject transaction only of
the General Corporation Law of the State of Delaware, including statutory and
reported decisional law thereunder, and we express no opinion with respect to
the applicability thereto, or the effect thereon, of the laws of any other
jurisdiction or, in the case of Delaware, any other laws, or as to any matters
of municipal law or the laws of any local agencies within any state.

     Subject to the foregoing, it is our opinion that the Shares have been duly
authorized, and, upon issuance, delivery and payment therefor in the manner
contemplated by the Registration Statement, will be validly issued, fully paid
and nonassessable.

     We consent to your filing this opinion as an exhibit to the Registration
Statement and to the reference to our firm contained under the heading "Legal
Matters."

                                             Very truly yours,

                                             /s/  LATHAM & WATKINS