PROCEPT, INC.

                                  PROCEPT, INC.

                       EXTENSION TO THE BOARD OF DIRECTORS
                    CONSULTING AND CONFIDENTIALITY AGREEMENT

THIS EXTENSION TO THE BOARD OF DIRECTORS CONSULTING AND CONFIDENTIALITY
AGREEMENT (the "Extension") is made as of this 3rd Day of December, 1998 (the
"Effective Date") by and between PROCEPT, INC., a Delaware corporation (the
"Company") and Xxxx X. Xxxxxx, M.D. (the "Consultant").

WHEREAS, the Company and the Consultant have entered into a Consulting and
Confidentiality Agreement dated as of January 1, 1998 (the "Agreement");

WHEREAS, the Company and the Consultant wish to extend the Initial Term for an
additional period of one year(s) commencing January 1, 1999 and ending on
December 31, 1999 (the "Extension Term");

NOW, THEREFORE, the Company and the Consultant, in consideration of the mutual
promises contained herein, hereby agree as follows:

1.      DEFINITIONS
        -----------

        Capitalized terms used herein and not otherwise defined herein shall
        have the respective meanings set forth in the Agreement.

2.      EXTENSION
        ---------

        2.1    Engagement. The Company hereby retains the Consultant and the
               Consultant hereby agrees to perform the services described in
               Sections 2.1 and 2.2 of the Agreement for the Extension Term.

        2.2    Incorporation of Agreement Provisions. Except as modified herein,
               the Company and Consultant agree that all of the provisions of
               the Agreement are incorporated herein and shall apply to the
               Consultancy during the Extension Term with the same force and
               effect as if set forth herein.

3.      REPRESENTATION, WARRANTIES AND COVENANTS
        ----------------------------------------

        Consultant hereby represents, warrants and covenants to the Company that
        the Consultant is under no contractual or other restriction or
        obligation which is inconsistent with his execution of this Extension or
        the performance of his duties hereunder and that, during the Extension
        Term, Consultant will not enter into any agreement either written or
        oral in conflict with this Extension.

The Consultant and the Company have executed and delivered this Extension as a
document under seal as of the Effective Date.


                                                  
PROCEPT, INC.                                        CONSULTANT:

By: /s/ Xxxx X. Xxx                                   /s/ Xxxx X. Xxxxxx
   -------------------------------                   ---------------------------
    Xxxx X. Xxx, President and CEO                   Xxxx X. Xxxxxx, M.D.


                                                     SSN: ______________________