EXHIBIT 5.1


                                    May 3, 1999


AdForce, Inc.
10590 North Tantau Avenue
Cupertino, California 95014

Gentlemen/Ladies:

     At your request, we have examined the Registration Statement on Form S-1
(File Number 333-73231) (the "REGISTRATION STATEMENT") filed by you with the
Securities and Exchange Commission (the "COMMISSION") on or about March 2, 1999,
as subsequently amended in connection with the registration under the Securities
Act of 1933, as amended, of an aggregate of 5,175,000 shares of your Common
Stock (the "STOCK").

     In rendering this opinion, we have examined the following:

     (1)  your registration statement on Form 8-A to be filed with the 
          Commission on or about May 4;

     (2)  the Registration Statement, together with the Exhibits filed as a part
          thereof;

     (3)  the prospectuses prepared in connection with the Registration
          Statement;

     (4)  the minutes of meetings and actions by written consent of the
          stockholders and Board of Directors that are contained in your minute
          books and the minute books of your predecessor, Imgis, a California
          corporation ("IMGIS CALIFORNIA"), that are in our possession;

     (5)  the stock records for both you and Imgis California that you have
          provided to us (consisting of a list of Stockholders and photocopies 
          of stock certificates and a list of option and warrant holders 
          respecting your capital stock and of any other rights to purchase 
          capital stock verifying the number of such issued and outstanding 
          securities); and

     (6)  a Management Certificate addressed to us and dated of even date
          herewith executed by the Company containing certain factual and other
          representations.

     In our examination of documents for purposes of this opinion, we have
assumed, and express no opinion as to, the genuineness of all signatures on
original documents, the authenticity and completeness of all documents submitted
to us as originals, the conformity to originals and completeness of all
documents submitted to us as copies, the legal capacity of all natural persons
executing the same, the lack of any undisclosed termination, modification,
waiver or amendment to any document reviewed by us and the due authorization,
execution and delivery of all documents where due authorization, execution and
delivery are prerequisites to the effectiveness thereof.




AdForce, Inc.
May 3, 1999
Page 2


     As to matters of fact relevant to this opinion, we have relied solely upon
our examination of the documents referred to above and have assumed the current
accuracy and completeness of the information obtained from public officials and
records referred to above.  We have made no independent investigation or other
attempt to verify the accuracy of any of such information or to determine the
existence or non-existence of any other factual matters; HOWEVER, we are not
aware of any facts that would cause us to believe that the opinion expressed
herein is not accurate.

     We are admitted to practice law in the State of California, and we express
no opinion herein with respect to the application or effect of the laws of any
jurisdiction other than the existing laws of the United States of America and
the State of California and (without reference to case law or secondary sources)
the existing Delaware General Corporation Law.

     In connection with our opinion expressed below, we have assumed that, at or
prior to the time of the delivery of any shares of the Stock, the Registration
Statement and the registration statement on Form 8-A will have been declared 
effective under the Securities Act of 1933, as amended, that the registration 
will apply to such shares of the Stock and will not have been modified or 
rescinded and that there will not have occurred any change in law affecting 
the validity or enforceability of such shares of the Stock.

     Based upon the foregoing, it is our opinion that the up to 5,175,000 shares
of the Stock to be issued and sold by you, when issued and sold in accordance in
the manner referred to in the relevant Prospectus associated with the
Registration Statement, will be validly issued, fully paid and nonassessable.

     We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to all references to us, if any, in the
Registration Statement, the Prospectus constituting a part thereof and any
amendments thereto.

     This opinion speaks only as of its date and we assume no obligation to
update this opinion should circumstances change after the date hereof.  This
opinion is intended solely for your use as an exhibit to the Registration
Statement for the purpose of the above sale of the Stock and is not to be relied
upon for any other purpose.

                                        Very truly yours,

                                        FENWICK & WEST LLP

                                        By:
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