<PAGE>
 
                                 AMENDMENT TO
                         REGISTRATION RIGHTS AGREEMENT

          THIS AGREEMENT is made this 16th day of December, 1996, by and among
Boston Communications Group, Inc. (the "Company") and Michael J. Buchel and
Zuyus Investment Company (together the "Stockholders" and individually each a
"Stockholder").

          WHEREAS, the parties were parties to a Registration Rights Agreement,
dated February 29, 1996 (the "Agreement") pursuant to which the Stockholders
were granted "piggyback" registration rights; and

          WHEREAS, the parties desire to amend the Agreement as hereinafter set
forth:

          NOW, THEREFORE, the parties do agree as follows:

          1.  The Company agrees that the shares now held by the Stockholders
(the "Shares") shall be registered by the Company under the Securities Act of
1933, as amended (the "Act"), pursuant to an S-3 Registration, as soon as the
Company can so register such Shares.  Prior to such registration or until such
time as the Stockholder may freely transfer Shares pursuant to Rule 144 or any
other exemption from registration, the Company agrees to purchase from any
Stockholder who desires to sell some or all of his Shares, such number of Shares
as such Stockholder shall notify the Company in writing of his intent to sell.
The price upon which the Company shall purchase shall be the closing price on
the Nasdaq National Market on the day preceding the date of receipt by the
Company of the Stockholder's notice of intent to sell.  The Stockholder shall
deliver to the Company a duly executed stock power with respect to such Shares
to be sold, and the Company shall thereupon make payment to the Stockholder by
certified check or bank check, or by wire transfer, of the full purchase price,
without fee or deduction therefrom.

          2.  The obligation of the Company to purchase Shares from a
Stockholder shall terminate upon the earlier to occur of (i) the effective date
of the registration statement registering the Shares under the Act, allowing the
Stockholder to freely transfer the Shares, or (ii) such time as the Stockholder
may freely transfer Shares pursuant to Rule 144 or any other exemption from
registration, which the parties anticipate to be February 29, 1998.

          3.  This repurchase agreement shall not supersede the Company's
Insider Trading Policy.  This Policy applies to all employees of director level
and above, and any other employees in possession of material inside information
and prohibits purchase or sale of the Company's stock during the period from two
weeks prior to the end of any fiscal quarter until the third business day after
the public release by the Company of earnings for that quarter.  (Thus, for
example, no purchase or sale of the Company's stock may be made during the
period from two weeks prior to the end of December until the third business day
after the release of earnings for the quarter, which is anticipated to
<PAGE>
 
Amendment to
Registration Rights
Agreement
December 16, 1996


be made in the first or second week of February, 1997.  Similarly, no purchase
or sale of the Company's stock may be made during the period from two weeks
prior to the end of March until the third business day after the release of
earnings for the first quarter.)  Provided, however, that if for any reason,
either Stockholder ceases to be an officer of the Company, then he or his estate
would have the right to sell his Shares free of the constraints of this Policy
to the Company or in the open market pursuant to Paragraph 1, above.

          4.  This agreement may be signed by the Stockholders in counterparts,
all of which shall constitute one and the same agreement.


          IN WITNESS WHEREOF, the parties have duly executed this Agreement as
of the day and year first above written.

                              BOSTON COMMUNICATIONS
                              GROUP, INC.


                              By: /s/George K. Hertz
                                  -----------------------         
                                  President


                                /s/ Michael J. Buchel
                              ---------------------------         
                              Michael J. Buchel


                              Zuyus Investment Company


                              By: /s/ Peter T. Zuyus, Sr.
                                  -----------------------       
                                  Peter T. Zuyus, Sr.

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