<PAGE>

                              STOCKHOLDER AGREEMENT

      AGREEMENT dated November 9, 1999, among Cordiant Communications Group plc,
a company organized under the laws of England and Wales ("Cordiant"),
Healthworld Acquisition Corporation, a Delaware corporation and a direct wholly
owned subsidiary of Cordiant ("Sub"), and William Butler (the "Stockholder").

                              W I T N E S S E T H:

      WHEREAS, concurrently herewith, Cordiant, Sub, and Healthworld
Corporation, a Delaware corporation (the "Company"), are entering into an
Agreement and Plan of Merger (as such agreement may hereafter be amended from
time to time, the "Merger Agreement"), pursuant to which Sub will be merged with
and into the Company and the Company shall continue as the surviving corporation
(the "Merger");

      Whereas, the Stockholder Beneficially Owns, as of the date hereof, 520,070
shares (the "Shares") of common stock, $.01 par value per share, of the Company
(the "Common Stock"); and

      WHEREAS, as an inducement and a condition to entering into the Merger
Agreement, Cordiant and Sub have required that the Stockholder agree, and the
Stockholder has agreed, to enter into this Agreement;

      NOW, THEREFORE, in consideration of the foregoing and the mutual premises,
representations, warranties, covenants and agreements contained herein, the
parties hereto, intending to be legally bound, hereby agree as follows:

      1. Definitions. Unless other defined herein, all capitalized terms used
herein shall have the meanings given to such terms in the Merger Agreement. For
purposes of this Agreement:

            (a) "Beneficially Own" or "Beneficial Ownership" with respect to any
securities shall mean having "beneficial ownership" of such securities (as
determined pursuant to Rule 13d-3 under the Securities Exchange Act of 1934, as
amended (the "Exchange Act")), including pursuant to any agreement, arrangement
or understanding, whether or not in writing.

      Without duplicative counting of the same securities by the same holder,
securities Beneficially Owned by a Person shall include securities Beneficially
Owned by all other Persons with whom such Person would constitute a "group" as
within the meanings of Section 13(d)(3) of the Exchange Act.

            (b) "Exchange Rate" means the average currency exchange rate of
pounds sterling to US dollars based upon the noon buying rate in the City of New
York for cable transfers in foreign currencies as announced by the Federal
Reserve Bank of New York for
<PAGE>

customs purposes over the 10 consecutive Trading Days ending on the day on which
the Stock Options are exercised pursuant to Section 3.

            (c) "Parent Share Value" shall mean the product of (x) the average
of the closing middle market quotation of a Parent Share on the LSE as reported
in the Daily Official List of the London Stock Exchange for each of the ten
consecutive Trading Days ending on the day on which the Stock Options are
exercised pursuant to Section 3 multiplied by (y) Exchange Rate.

            (d) "Parent Shares" shall mean the ordinary shares, with a nominal
value of U.K. fifty pence each ("Ordinary Shares"), of Cordiant (including any
options or other rights to receive Ordinary Shares) and the American Depositary
Shares, each representing the right to receive five Ordinary Shares ("ADSs").

            (e) "Person" shall mean an individual, corporation, partnership,
limited liability company, joint venture, association, trust, unincorporated
organization or other entity.

            (f) "Share Value" shall be determined as follows:

            (i) if the Parent Share Value is equal to or greater than $2.5054
      and equal to or less than $3.4838, the Share Value shall be $20.00;

            (ii) if the Parent Share Value is greater than $3.4838, the Share
      Value shall be $23.00; and

            (iii) if the Parent Share Value is less than $2.5054, the Share
      Value shall be $17.00.

            (g) "Trading Day" shall mean any day on which securities are traded,
with respect to ADSs, on the New York Stock Exchange, Inc. and with respect to
Ordinary Shares, on the London Stock Exchange Limited.

      2. Provisions Concerning Common Stock. (a) The Stockholder hereby agrees
that during the period described in clause (b) below, at any meeting of the
holders of Common Stock of the Company, however called, or in connection with
any written consent of the holders of Common Stock of the Company, the
Stockholder shall vote (or cause to be voted) the Shares of Common Stock of the
Company, (i) in favor of the Merger, the execution and delivery by the Company
of the Merger Agreement and the approval of the terms thereof and each of the
other actions contemplated by the Merger Agreement and this Agreement and any
actions required in furtherance thereof and hereof; (ii) against any action or
agreement that would result in a breach in any material respect of any covenant,
representation or warranty or any other obligation or agreement of the Company
under the Merger Agreement or this Agreement; and (iii) except as otherwise
agreed to in writing in advance by Cordiant, against the following actions
(other than the Merger and the transactions contemplated by the Merger
Agreement): (A) any extraordinary corporate transaction, such as a merger,
consolidation or other business combination involving the Company or its
Subsidiaries; (B) a sale, lease or transfer of a material amount of assets of
the


                                      -2-
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Company or its Subsidiaries, or a reorganization, recapitalization, dissolution
or liquidation of the Company or its Subsidiaries; (C) any change in a majority
of the persons who constitute the board of directors of the Company; (D) any
change in the present capitalization of the Company or any amendment of the
Company's Certificate of Incorporation or Bylaws; (E) any other material change
in the Company's corporate structure or business; or (F) any other action
involving the Company or its Subsidiaries which is intended, or could reasonably
be expected, to materially impede, interfere with, delay, postpone, or
materially adversely affect the Merger and the transactions contemplated by this
Agreement and the Merger Agreement. The Stockholder shall not enter into any
agreement or understanding with any Person the effect of which would be
inconsistent with or violative of the provisions and agreements contained in
this Section 2.

      (b) The obligations of the Stockholders under clauses (i), (ii) and
(iii)(C), (D), (E) and (F) of this Section 2 shall terminate on the earlier to
occur of the Effective Time and the termination of the Merger Agreement in
accordance with its terms. The obligations of the Stockholder under clause
(iii)(A) and (B) of this Section 2 shall terminate on the earlier to occur of
the Effective Time and 120 days after the termination of the Merger Agreement in
accordance with its terms (unless the Merger Agreement is terminated by reason
of the failure to obtain Parent Shareholders' Approval in which case the
Stockholder's obligations under this Section 2 shall terminate simultaneously
with the termination of the Merger Agreement).

      3. Option to Purchase. In order to induce Cordiant and Sub to enter into
the Merger Agreement, the Stockholder hereby grants to Sub an irrevocable option
(the "Stock Options") to purchase, all, and not less than all, of the Shares at
a purchase price per share equal to the Share Value, payable in cash (the
"Purchase Price"), solely upon, and subject to, the terms and conditions set
forth below. The Stock Options may only be exercised if Sub simultaneously
exercises all other options held by it to purchase all, and not less than all,
of the shares of Common Stock covered by such options. The Stock Options shall
become exercisable solely in the event that the Merger Agreement is terminated
pursuant to (i) Section 9.1(b)(ii) thereof, but only if the basis for such
termination is the failure to obtain the Company Stockholder Approval or (ii)
Section 9.1(b)(iii) thereof, but only if the basis for such termination is a
breach by the Company, or the Stockholder materially breaches any agreement
contained in this Agreement, in which event the Stock Options shall, in any such
case, become immediately exercisable at any time and from time to time upon such
termination or upon Cordiant and Sub being informed of such breach, as the case
may be, and until the date which is 20 days after the date of such termination
or the date on which Cordiant and Sub are informed of such breach, as the case
may be, provided, that if at the expiration of such 20-day period the Stock
Options cannot be exercised by reason of any preliminary or final injunction or
other order issued by any court or governmental, administrative or regulatory
agency or authority prohibiting the exercise of the Stock Options pursuant to
this Agreement, or because all waiting periods under the Hart-Scott-Rodino
Antitrust Improvements Act of 1976, as amended (the "HSR ACT"), required for the
purchase of the Shares upon such exercise shall not have expired or been waived,
the Stock Options shall be exercisable until 10 business days after the later of
the date on which such impediment to exercise shall have been removed or shall
have become final and not subject to appeal. In all other instances, the Stock
Options shall terminate upon the termination of the Merger Agreement. In the
event that Cordiant wishes to exercise the Stock Options, Cordiant


                                      -3-
<PAGE>

shall send a written notice (the "Notice") to the Stockholder identifying the
place (which shall be in New York City for each Stockholder who is a resident of
the United States and in London for each Stockholder who is a resident of the
United Kingdom) and date (not less than two business days nor greater than ten
business days from the date of the Notice) for the closing of such purchase. At
such closing, Cordiant shall receive certificates for the Shares, duly endorsed
for transfer, and shall make payment therefor by wire transfer of immediately
available funds.

      4. Disposition of Parent Shares.

            (a) Restrictions on Disposition. The Stockholder hereby agrees,
except as permitted in this Section 4(a) and Section 4(b) below, not to directly
or indirectly, offer to sell, contract to sell, transfer, assign, cause to be
redeemed or otherwise sell or dispose of any of the Parent Shares (collectively
a "Disposition") received by the stockholder in connection with the Merger
without the prior written consent of Cordiant. Notwithstanding anything to the
contrary provided in this Agreement, the Stockholder shall have the right to
transfer Parent Shares (i) to any Family Member, (ii) to the trustee or trustees
of a trust solely (except for remote contingent interests) for the benefit of
the Stockholder and/or one or more Family Members and/or a charitable
organization (a "Family Member Trust"), (iii) to a foundation created or
established by the Stockholder, or any other charitable organization, (iv) to a
corporation of which the Stockholder and/or any Family Member and/or any Family
Member Trust owns all of the outstanding capital stock, (v) to a limited
liability company of which the Stockholder and/or any Family Member and/or any
Family Member Trust owns all of the outstanding membership interests, (vi) to a
partnership of which the Stockholder and/or any Family Member and/or any Family
Member Trust owns all of the partnership interests, (vii) to the executor,
administrator or personal representative of the estate of the Stockholder or any
other Family Member, or (viii) to any guardian, trustee or conservator appointed
with respect to the assets of the Stockholder, provided, that in the case of any
such transfer, the transferee shall execute an agreement to be bound by the
terms of this Agreement (each such transfer, a "Permitted Transfer" and,
collectively, the "Permitted Transfers"). For purposes of this Agreement,
"Family Member" shall mean (a) the Stockholder's spouse, if living with the
Stockholder, (b) any one of the following: the Stockholder's father, mother,
issue, brother or sister, and the issue of a brother or sister, and (c) the
spouse of any Family Member described in (b) above, if the spouse shall be
living with that Family Member. The Stockholder hereby agrees and consents to
the entry of stop transfer instructions with Cordiant's transfer agent against
the transfer of such Parent Shares except in compliance with this Agreement.
Notwithstanding the foregoing, the Stockholder may pledge, hypothecate or
otherwise grant a security interest in all or a portion of the Parent Shares
beneficially owned by him during the term of this Agreement; provided, however,
that any Person receiving such Parent Shares shall be subject to all of the
restrictions on Disposition of such Parent Shares imposed by this Agreement to
the same extent as the Stockholder.

            (b) Permitted Dispositions. The Stockholder may not effect any
Disposition of Parent Shares received by the Stockholder in connection with the
Merger except as follows: (i) during the twelve-month period immediately
following the Effective Time the Stockholder may effect the Disposition of not
more than 15% of the Parent Shares Beneficially Owned by the Stockholder and
(ii) during the twenty-four-month period immediately following the


                                      -4-
<PAGE>

Effective Time (the "Period"), the Stockholder may effect the Disposition of not
more than 55% of the Parent Shares Beneficially Owned by the Stockholder. Upon
the expiration of the Period, the Stockholder may effect the Dispositions of all
or any portion of the Parent Shares Beneficially Owned by him subject to any
applicable restrictions under the Federal Securities Law and restrictions of
general application under English law, the Listing Rules of the London Stock
Exchange, if applicable, and Cordiant's policies made pursuant to such rules
regarding dealings in Parent Shares by directors and relevant employees of
Cordiant and its subsidiaries, if applicable. Notwithstanding anything to the
contrary contained in this Section 4, the Stockholder hereby agrees that for the
period commencing at the Effective Time and ending on the date which is 180 days
after the expiration of the Period, the Stockholder shall give Cordiant 1
business day prior written notice of any intended Disposition of Parent Shares
to be made by the Stockholder and at the request of Cordiant agrees to effect
such Disposition through brokers or other financial intermediaries designated by
Cordiant to maintain an orderly trading market for the Parent Shares, provided
that such financial intermediary agrees to effect and does effect the
Disposition in a reasonable period following such notice.

      5. Representations and Warranties of the Stockholder. The Stockholder
hereby represents and warrants to each of Cordiant and Sub as follows:

            (a) Ownership of Shares. The Stockholder is the record holder of or
Beneficially Owns the Shares. On the date hereof, the Shares constitute all of
the shares of Common Stock owned of record or Beneficially Owned by the
Stockholder (excluding any Stock Options (as defined in the Merger Agreement)
held by the Stockholder). The Stockholder has sole voting power and sole power
to issue instructions with respect to the matters set forth in Section 2 hereof,
sole power of disposition, sole power of conversion, sole power to exercise
dissenters' rights and sole power to agree to all of the matters set forth in
this agreement, in each case with respect to all of the Shares, with no
limitations, qualifications or restrictions on such rights, subject to
applicable securities laws and the terms of this Agreement.

            (b) Power; Binding Agreement. The Stockholder has the legal
capacity, power and authority to enter into and perform all of his obligations
under this Agreement. The execution, delivery and performance of this Agreement
by the Stockholder will not violate any other Agreement to which the Stockholder
is a party including, without limitation, any voting agreement, shareholders
agreement or voting trust. This Agreement has been duly and validly executed and
delivered by the Stockholder and constitutes a valid and binding agreement of
the Stockholder, enforceable against the Stockholder in accordance with its
terms except that such enforceability (i) may be limited by bankruptcy,
insolvency, moratorium or other similar laws relating to the enforcement of
creditors' rights generally and (ii) is subject to general principles of equity
and discretion of the court before which any proceedings seeking injunctive
relief or specific performance may be sought. There is no beneficiary or holder
of a voting trust certificate or other interest of any trust of which the
Stockholder is trustee whose consent is required for the execution and delivery
of this agreement or the consummation by the Stockholder of the transactions
contemplated hereby. If the Stockholder is married and the Stockholder's Shares
constitute community property, this agreement has been duly authorized, executed
and delivered by, and constitutes a valid and binding agreement of, the
Stockholder's


                                      -5-
<PAGE>

spouse, enforceable against such Person in accordance with its terms except that
such enforceability (i) may be limited by bankruptcy, insolvency, moratorium or
other similar laws relating to the enforcement of creditors' rights generally
and (ii) is subject to general principles of equity and discretion of the court
before which any proceedings seeking injunctive relief or specific performance
may be sought.

            (c) No Conflicts. Except for filings, permits, authorizations,
consents and approvals under the HSR Act and the Securities Act of 1933, if
applicable, (A) no filing with, and no permit, authorization, consent or
approval of, any state or federal public body or authority is necessary for the
execution of this Agreement by the Stockholder and the consummation by the
Stockholder of the transactions contemplated hereby and (B) none of the
execution and delivery of this Agreement by the Stockholder, the consummation by
the Stockholder of the transactions contemplated hereby or compliance by the
Stockholder with any of the provisions hereof shall, in a manner which would be
material and adverse to the ability of the Stockholder to consummate the
transactions contemplated hereby or to comply with the terms hereof, result in a
violation or breach of, or constitute (with or without notice or lapse of time
or both) a default (or give rise to any third party right of termination,
cancellation, material modification or acceleration) under any of the terms,
conditions or provisions of any note, bond, mortgage, indenture, license,
contract, commitment, arrangement, understanding, agreement or other instrument
or obligation of any kind to which the Stockholder is a party or by which the
Stockholder or any of the Stockholder's properties or assets may be bound, or
(3) violate any order, writ, injunction, decree, judgment, order, statute, rule
or regulation applicable to the Stockholder or any of the Stockholder's
properties or assets.

            (d) No Encumbrances. Except as applicable in connection with the
transactions contemplated hereby or as set forth on Schedule B attached hereto,
the Shares and the certificates representing the Shares are now, and at all
times during the term hereof will be, held by the Stockholder, or by a nominee
or custodian for the benefit of the Stockholder, free and clear of all liens,
claims, security interests, proxies, voting trusts or agreements, understandings
or arrangements or any other encumbrances whatsoever, except for any such
encumbrances or proxies arising hereunder in favor of Cordiant.

            (e) No Finder's Fees. No broker, investment banker, financial
adviser or other person is entitled to any broker's, finder's, financial
adviser's or other similar fee or commission in connection with the transactions
contemplated hereby based upon arrangements made by or on behalf of the
Stockholder other than Bear Stearns & Co. Inc., the fees and expenses of which
shall be paid by the Company.

            (f) Reliance by Cordiant and Sub. The Stockholder understands and
acknowledges that Cordiant and Sub are entering into the Merger Agreement in
reliance upon the Stockholder's execution and delivery of this Agreement.

      6. Additional Covenants of the Stockholder. The Stockholder hereby
covenants to each of Cordiant and Sub as follows:


                                      -6-
<PAGE>

            (a) No Solicitation. Subject to the provisions contained in Section
10 of this Agreement, the Stockholder shall not, in his capacity as such,
directly or indirectly, solicit (including by way of furnishing information) or
respond to any inquiries or the making of any proposal by any Person or entity
(other than Cordiant or any affiliate of Cordiant) with respect to the Company
that constitutes a Takeover Proposal. If the Stockholder receives any such
inquiry or proposal, then the Stockholder shall promptly inform Cordiant of the
existence thereof. The Stockholder will immediately cease and cause to be
terminated any existing activities, discussions or negotiations with any parties
conducted heretofore with respect to any of the foregoing.

            (b) Restriction on Transfer of Shares, Proxies and Non-Interference.
Beginning on the date hereof and ending on the later to occur of (A) last date
the Stock Options are exercisable pursuant to Section 3 hereof and (B) the date
that all of the Stockholder's obligations under Section 2 have terminated,
except as contemplated by this Agreement or the Merger Agreement, no Stockholder
shall, directly or indirectly, (i) offer for sale, sell, transfer, tender,
pledge, encumber, assign or otherwise dispose of, or enter into any contract,
option or other arrangement or understanding with respect to or consent to the
offer for sale, sale, transfer, tender, pledge, encumbrance, assignment or other
disposition of, any or all of the Shares or any interest therein; (ii) except as
contemplated by this Agreement, grant any proxies or powers of attorney, deposit
any of the Shares into a voting trust or enter into a voting agreement with
respect to any of the Shares; or (iii) take any action that would make any
representation or warranty of the Stockholder contained herein untrue or
incorrect or have the effect of preventing or disabling the Stockholder from
performing the Stockholder's obligations under this Agreement. Notwithstanding
anything to the contrary provided in this Agreement, a Stockholder shall have
the right to make Permitted Transfers of Shares. The Stockholder agrees with,
and covenants to, Sub that beginning on the date hereof and ending on the last
date the Stock Options are exercisable pursuant to Section 3 hereof, the
Stockholder shall not request that the Company register the transfer (book-entry
or otherwise) of any certificate or uncertificated interest representing any of
the Shares, unless such transfer is made in compliance with this Agreement
(including the provisions of Section 2 hereof).

            (c) Additional Shares. The Stockholder agrees, while this Agreement
is in effect (i) to notify Cordiant and Sub promptly of the number of any shares
of Common Stock acquired by the Stockholder after the date hereof (the
"Additional Shares") and (ii) to vote such Additional Shares in accordance with
Section 2 hereof. Such Additional Shares shall also be subject to the Stock
Option granted to Sub pursuant to Section 3 hereof and the restriction contained
in Section 6(b)(i) and (ii) above.

      7. Representations and Warranties of Cordiant and Sub. Cordiant and Sub
hereby covenant, represent and warrant to the Stockholder that each of Cordiant
and Sub has the legal capacity, power and authority to enter into and perform
all of such party's obligations under this Agreement; the execution, delivery
and performance of this Agreement by Cordiant and Sub will not violate or result
in a breach of any other material agreement to which Cordiant or Sub is a party;
the execution and delivery of this Agreement and the consummation of the
transactions contemplated hereby (i) have been duly authorized by the board of
directors of Cordiant and Sub, and (ii) do not and will not violate any
provision of the certificate of incorporation or by-laws of


                                      -7-
<PAGE>

Cordiant or Sub; and this Agreement has been duly and validly executed and
delivered by each of Cordiant and Sub and constitutes a valid and binding
agreement of such party, enforceable against such party in accordance with its
terms.

      8. Further Assurances. From time to time, at the other party's request and
without further consideration, each party hereto shall execute and deliver such
additional reasonable documents and take all such further reasonable lawful
action as may be necessary or desirable to consummate and make effective, in the
most expeditious manner practicable, the transactions contemplated by this
Agreement.

      9. Termination; Expenses and Fee. (a) The covenants and agreements
contained herein with respect to the Shares shall terminate (i) in the event the
Merger Agreement is terminated in accordance with its terms, upon such
termination, except that the provisions of Sections 2, 3 and 6(b) hereof shall
survive any such termination solely in accordance with their terms and (ii) in
the event the Merger is consummated, at the Effective Time, except that the
provisions of Section 4 hereof shall survive any such termination, provided, in
each case, that the provisions of Section 12 and Section 13 hereof shall survive
any termination of this Agreement, and provided, further, that no termination of
this Agreement shall relieve any party of liability for a breach hereof.

            (b) Each party shall bear its own expenses in connection with this
Agreement and the transactions contemplated hereby.

      10. Stockholder Capacity. The Stockholder is not executing this Agreement
and does not make any agreement or understanding herein in his or her capacity
as a director or officer of the Company and nothing contained herein shall limit
or affect any actions taken by the Stockholder in his capacity as a director or
officer of the Company to the extent such action is permitted by, or not
prohibited by, the Merger Agreement, and none of such actions in such capacities
shall be deemed to constitute a breach of this Agreement. The Stockholder signs
solely in his capacity as the record and beneficial owner of, or the trustee of
a trust whose beneficiaries are the beneficial owners of, the Shares.

      11. Sophistication. The Stockholder acknowledges that he is an informed
and sophisticated investor and, together with his advisors, has undertaken such
investigation as they have deemed necessary, including the review of the Merger
Agreement and this Agreement, to enable the Stockholder to make an informed and
intelligent decision with respect to the Merger Agreement and this Agreement and
the transactions contemplated thereby and hereby.

      12. Confidentiality. Each of the parties hereto recognizes that successful
consummation of the transactions contemplated by this Agreement may be dependent
upon confidentiality with respect to the matters referred to herein. In this
connection, pending public disclosure thereof, each party hereby agrees not to
disclose or discuss such matters with anyone not a party to this Agreement or
the Merger Agreement (other than such party's counsel and advisors, if any)
without the prior written consent of the other party, except for filings
required pursuant to the Exchange Act and the rules and regulations thereunder
or disclosures such party's counsel advises are necessary in order to fulfill
such party's obligations imposed by law, in


                                      -8-
<PAGE>

which event such party shall give notice of such disclosure to the other party
as promptly as practicable so as to enable the other party to seek a protective
order from a court of competent jurisdiction with respect thereto.

      13. Miscellaneous.

            (a) Entire Agreement. This Agreement and the Merger Agreement
constitute the entire agreement between the parties with respect to the subject
matter hereof and supersede all other prior agreements and understandings, both
written and oral, between the parties with respect to the subject matter hereof.

            (b) Certain Events. The Stockholder agrees that this Agreement and
the obligations hereunder shall attach to the Stockholder's Shares and shall be
binding upon any person or entity to which legal or beneficial ownership of such
Shares shall pass, whether by operation of law or otherwise, including, without
limitation, the Stockholder's heirs, guardians, administrators or successors,
provided, that following the Effective Time, this Agreement shall not be binding
on any purchaser of Shares in a transaction made in compliance with Section
4(b), other than Permitted Transfers. Notwithstanding any transfer of Shares,
the transferor shall remain liable for the performance of all obligations under
this Agreement of the transferor.

            (c) Change in Control. In the event that after the Effective Time
(i) any Person or group of Persons acting in concert (as defined in the City
Code on Take-overs and Mergers in the United Kingdom) acquires an interest in
the equity share capital of Cordiant (an "Acquiring Person") and, immediately
following such acquisition, such person, or group, holds shares entitled to
exercise more than 50% of the votes which may be cast at a general meeting of
Cordiant or (ii) a majority of the board of directors of Cordiant immediately
prior to such Person becoming an Acquiring Person, cease to thereafter
constitute a majority of the board of directors of Cordiant (other than through
elections of directors whose nomination for election by the shareholders of
Cordiant were approved by the vote of a majority of directors of Cordiant who
were either directors prior to a Person becoming an Acquiring Person or whose
election or nomination for election was so previously approved), then the
restrictions on Dispositions contained in Section 4, shall terminate without any
action on the part of any party hereto.

            (d) Assignment. This Agreement shall not be assigned by operation of
law or otherwise without the prior written consent of the other party, provided,
that Cordiant or Sub may assign, in its sole discretion, its rights and
obligations hereunder to any direct or indirect wholly owned subsidiary of
Cordiant, but no such assignment shall relieve Cordiant or Sub of its
obligations hereunder if such assignee does not or cannot perform such
obligations.

            (e) Amendments, Waivers, Etc. This Agreement may not be amended,
changed, supplemented, waived or otherwise modified or terminated, except upon
the execution and delivery of a written agreement executed by the party to be
charged thereby or, with respect to termination, as otherwise provided herein.

            (f) Notices. All notices, requests, claims, demands and other
communications hereunder shall be in writing and shall be given (and shall be
deemed to have been duly received


                                      -9-
<PAGE>

if so given) by hand delivery, telegram, telex or telecopy, or by mail
(registered or certified mail, postage prepaid, return receipt requested) or by
any courier service, such as Federal Express, providing proof of delivery. All
communications hereunder shall be delivered to the respective parties at the
following addresses:

      If to the Stockholder:  William Butler
                              [Address]
                              Attention:
                              Facsimile:

      and

      If to Cordiant or
      Sub to:                 Cordiant Communications Group plc
                              121-141 Westbourne Terrace
                              London W2 6JR
                              Deputy Finance Director
                              Facsimile: +44-171-262-4300

      copy to:                White & Case LLP
                              1155 Avenue of the Americas
                              New York, New York  10036-2787
                              Attention: Timothy B. Goodell, Esq.
                              Facsimile: (212) 354-8113

or to such other address as the person to whom notice is given may have
previously furnished to the others in writing in the manner set forth above.

            (g) Severability. Whenever possible, each provision or portion of
any provision of this Agreement will be interpreted in such manner as to be
effective and valid under applicable law but if any provision or portion of any
provision of this Agreement is held to be invalid, illegal or unenforceable in
any respect under any applicable law or rule in any jurisdiction, such
invalidity, illegality or unenforceability will not affect any other provision
or portion of any provision in such jurisdiction, and this Agreement will be
reformed, construed and enforced in such jurisdiction as if such invalid,
illegal or unenforceable provision or portion of any provision had never been
contained herein.

            (h) Specific Performance. Each of the parties hereto recognizes and
acknowledges that a breach by it of any covenants or agreements contained in
this Agreement will cause the aggrieved party to sustain damages for which it
would not have an adequate remedy at law for money damages, and therefore each
of the parties hereto agrees that in the event of any such breach the aggrieved
party shall be entitled to the remedy of specific performance of such covenants
and agreements and injunctive and other equitable relief in addition to any
other remedy to which it may be entitled, at law or in equity.


                                      -10-
<PAGE>

            (i) Remedies Cumulative. All rights, powers and remedies provided
under this Agreement or otherwise available in respect hereof at law or in
equity shall be cumulative and not alternative, and the exercise of any thereof
by any party shall not preclude the simultaneous or later exercise of any other
such right, power or remedy by such party.

            (j) No Waiver. The failure of any party hereto to exercise any
right, power or remedy provided under this Agreement or otherwise available in
respect hereof at law or in equity, or to insist upon compliance by any other
party hereto with its obligations hereunder, and any custom or practice of the
parties at variance with the terms hereof, shall not constitute a waiver by such
party of its right to exercise any such or other right, power or remedy or to
demand such compliance.

            (k) No Third Party Beneficiaries. This Agreement is not intended to
be for the benefit of, and shall not be enforceable by, any person or entity who
or which is not a party hereto.

            (l) Governing Law. This Agreement shall be governed and construed in
accordance with the laws of the State of New York, without giving effect to the
principles of conflicts of law thereof.

            (m) Jurisdiction. Each party hereby irrevocably submits to the
exclusive jurisdiction of the Court of Chancery in the State of Delaware or the
United States District Court for the Southern District of New York or any court
of the State of New York located in the City of New York in any action, suit or
proceeding arising in connection with this Agreement, and agrees that any such
action, suit or proceeding shall be brought only in such court (and waives any
objection based on forum non conveniens or any other objection to venue
therein); provided, however, that such consent to jurisdiction is solely for the
purpose referred to in this paragraph (1) and shall not be deemed to be a
general submission to the jurisdiction of said Courts or in the States of
Delaware or New York other than for such purposes. Each party hereto hereby
waives any right to a trial by jury in connection with any such action, suit or
proceeding.

            (n) Descriptive Headings. The descriptive headings used herein are
inserted for convenience of reference only and are not intended to be part of or
to affect the meaning or interpretation of this Agreement.

            (o) Counterparts. This Agreement may be executed in counterparts,
each of which shall be deemed to be an original, but all of which, taken
together, shall constitute one and the same Agreement.

                         [SIGNATURES BEGIN ON NEXT PAGE]


                                      -11-
<PAGE>

      IN WITNESS WHEREOF, Cordiant, Sub and the Stockholder have caused this
      Agreement to be duly executed as of the day and year first above written.

                                        CORDIANT COMMUNICATIONS GROUP PLC

                                        By: /s/ Arthur D'Angelo
                                            ------------------------------------
                                            Name: Arthur D'Angelo
                                            Title: Finance Director


                                        HEALTHWORLD ACQUISITION CORPORATION

                                        By: /s/ Arthur D'Angelo
                                            ------------------------------------
                                            Name: Arthur D'Angelo
                                            Title: President


                                        /s/ William Butler
                                        ----------------------------------------
                                        William Butler


                                      -12-