<PAGE>

Exhibit 10.13

                  THIS AMENDMENT, made this 23rd day of September, 1998, by
and between HEALTHWORLD CORPORATION, a Delaware corporation, with offices at
100 Avenue of the Americas, New York, New York 10013 (the "Company"), and
STUART DIAMOND, an individual residing at 22 Woodland Place, Great Neck, New
York 11021 (the "Employee"), amends that certain Employment Agreement, dated
as of August 18, 1997 (the "Employment Agreement"), between the Company and
the Employee. Capitalized terms not otherwise defined herein are used herein
as defined in the Employment Agreement.

                  WHEREAS, the Company and the Employee have previously
entered into the Employment Agreement;

                  WHEREAS, the parties hereto desire to amend the Employment
Agreement as set forth herein; and

                  WHEREAS, all terms and conditions of the Employment
Agreement, other than as specifically amended hereby, shall remain in full
force and effect;

                  NOW, THEREFORE, in consideration of the mutual covenants and
agreements herein contained, the parties hereto agree as follows:

                  1. Amendments to the Employment Agreement. Effective as of
the date hereof, the Employment Agreement is hereby amended as follows:

                  (a) Section 7.5 of the Employment Agreement is hereby
         amended by (i) inserting the words "other than upon the occurrence
         of, or within two years following, a Change in Control (as defined in
         Section 7.6(b)) of the Company" immediately after the phrase "for any
         reason whatsoever" contained therein, and (ii) replacing the words
         "six (6) months Base Salary" contained therein with the words "twelve
         (12) months Base Salary."

                  (b) Section 7.6 of the Employment Agreement is hereby
         deleted in its entirety and the following new Section 7.6 is hereby
         inserted in its place:

                           "7.6(a) Notwithstanding the foregoing, in the event
                  that the Employee's employment is terminated during the term
                  of this Agreement (i) by the Employee upon 30 days prior
                  written notice to the Company for Good Reason (as defined in
                  Section 7.6(c)), or (ii) by the Company (in such case such
                  termination shall be valid only upon receipt by the Employee
                  of 30 days prior written notice of such termination), in
                  either case within two years following a Change in Control
                  of the Company, the Employee shall be entitled to receive
                  (A) an amount equal to Employee's full Base Salary and all
                  other compensation (including, without limitation, any
                  bonuses) 


<PAGE>


                  accrued but not yet paid through the date of termination of
                  Employee's employment, (B) an amount, payable in cash by the
                  Company on the date of termination of Employee's employment,
                  equal to (i) Employee's annual cash bonus for the fiscal
                  year prior to the year in which Employee's employment is
                  terminated plus (ii) the greater of Employee's 18 months
                  Base Salary in effect immediately prior to the date of the
                  Change in Control of the Company or the Employee's 18 months
                  Base Salary in effect on the date of termination of
                  Employee's employment; provided, however, that in the event
                  that Employee's employment is terminated pursuant to this
                  Section 7.6(a) after the one-year anniversary but on or
                  prior to the two year anniversary following a Change in
                  Control of the Company, Employee shall only be entitled to
                  receive from the Company an amount equal to (x) Employee's
                  annual cash bonus for the fiscal year prior to the year in
                  which Employee's employment is terminated plus (y) twelve
                  months Base Salary (as determined in this clause (B)), (C)
                  any benefits then vested under any benefit plans and
                  otherwise payable in accordance with the provisions of the
                  applicable benefit plan and applicable laws, and (D)
                  continued coverage (net of any Employee contributions) to
                  the extent any such coverage was provided immediately prior
                  to the termination of Employee for medical, health, hospital
                  and disability insurance for a period of 12 months following
                  the date of termination of Employee's employment under the
                  benefit plans maintained by the Company or any of the
                  Company's United States subsidiaries for its senior
                  management or employees generally in accordance with the
                  terms thereof, or if the Company is unable to provide such
                  coverage under its benefit plans as they may from time to
                  time be in effect, the Company will provide or pay (without
                  gross-up for taxes), at the Company's sole discretion, for
                  coverage (net of any Employee contributions) having
                  substantially the same aggregate value as the coverage
                  provided under such plans.

                           (b) For purposes hereof, a "Change in Control" of
                  the Company shall occur or be deemed to have occurred only
                  if any of the following events occurs:

                           (i) any "person," as such term is used in Sections
                           13(d) and 14(d) of the Securities Exchange Act of
                           1934, as amended (the "Exchange Act") (other than
                           the Company, any trustee or other fiduciary holding
                           securities under an employee benefit plan of the
                           Company, or any corporation owned directly or
                           indirectly by the stockholders of the Company in
                           substantially the same proportion as the ownership
                           of stock of the Company), is or becomes the
                           "beneficial owner" (as defined in Rule 13d-3 under
                           the 


                                      2
<PAGE>


                           Exchange Act), directly or indirectly, of
                           securities of the Company representing more than
                           50% of the combined voting power of the Company's
                           then outstanding securities; or

                           (ii) individuals who, as of September 23, 1998 (the
                           "Effective Date"), constitute the Board of
                           Directors of the Company (as of the Effective Date,
                           the "Incumbent Board") cease for any reason to
                           constitute at least a majority of the Board of
                           Directors of the Company, provided that any person
                           becoming a director subsequent to the date hereof
                           whose election, or nomination for election by the
                           Company's stockholders, was approved by a vote of
                           at least a majority of the directors then
                           comprising the Incumbent Board (other than an
                           election or nomination of an individual whose
                           initial assumption of office is in connection with
                           an actual or threatened election contest relating
                           to the election of the directors of the Company, as
                           such terms are used in Rule 14a-11 of Regulation
                           14A under the Exchange Act) shall be, for purposes
                           of this Agreement, considered as though such person
                           were a member of the Incumbent Board; or 

                           (iii) the stockholders of the Company approve a
                           merger or consolidation of the Company with any
                           other corporation, other than (A) a merger or
                           consolidation which would result in the voting
                           securities of the Company outstanding immediately
                           prior thereto continuing to represent (either by
                           remaining outstanding or by being converted into
                           voting securities of the surviving entity) more
                           than 60% of the combined voting power of the voting
                           securities of the Company or such surviving entity
                           outstanding immediately after such merger or
                           consolidation or (B) a merger or consolidation
                           effected to implement a recapitalization of the
                           Company (or similar transaction) in which no
                           "person" (as hereinabove defined) acquires more
                           than 50% of the combined voting power of the
                           Company's then outstanding securities; or 

                           (iv) the stockholders of the Company approve a plan
                           of complete liquidation of the Company or an
                           agreement for the sale or disposition by the
                           Company of all or substantially all of the
                           Company's assets.

                           (c) As used herein, the term "Good Reason" means
                  the occurrence after a Change in Control of the Company of
                  any of the following circumstances:


                                      3
<PAGE>


                           (i) Any diminution in the Employee's position,
                           duties, responsibilities, title or office as in
                           effect immediately prior to a Change in Control;

                           (ii) Any reduction in the Employee's annual Base
                           Salary as in effect on the date hereof or as the
                           same may be increased from time to time;

                           (iii) The failure of the Company to continue in
                           effect any material compensation or benefit plan in
                           which the Employee participates immediately prior
                           to the Change in Control, unless an equitable
                           arrangement (embodied in an ongoing substitute or
                           alternative plan) has been made with respect to
                           such plan, or the failure by the Company to
                           continue the Employee's participation therein (or
                           in such substitute or alternative plan) on a basis
                           not materially less favorable, both in terms of the
                           amount of benefits provided and the level of the
                           Employee's participation relative to other
                           participants, as existed at the time of the Change
                           in Control or the failure by the Company to award
                           cash bonuses to its executives in amounts
                           substantially consistent with past practice in
                           light of the Company's financial performance;

                           (iv) the failure by the Company to continue to
                           provide the Employee with benefits substantially
                           similar to those enjoyed by the Employee under any
                           of the Company's insurance, medical, health and
                           accident, or disability plans in which the Employee
                           was participating at the time of the Change in
                           Control, the taking of any action by the Company
                           which would directly or indirectly materially
                           reduce any of such benefits, or the failure by the
                           Company to provide the Employee with the number of
                           paid vacation days to which he is entitled in
                           accordance with the Company" normal vacation policy
                           in effect at the time of the Change in Control or
                           in accordance with any agreement between the
                           Employee and the Company existing at the time of
                           the Change in Control;

                           (v) any requirement by the Company or of any person
                           in control of the Company that the location at
                           which the Employee performs his principal duties
                           for the Company at the time of the Change in
                           Control (the "Prior Location") be changed to a new
                           location outside a radius of 35 miles from such
                           Prior Location;


                                      4
<PAGE>


                           (vi) any requirement by the Company or of any
                           person in control of the Company that the Employee
                           travels on an overnight basis to an extent not
                           substantially consistent with his business travel
                           obligations immediately prior to a Change in
                           Control of the Company;

                           (vii) the failure of the Company to obtain a
                           satisfactory agreement from any successor to assume
                           and agree to perform this Agreement; or

                           (viii) any purported termination of the Employee's
                           employment which is not effected pursuant to this
                           Section 7.6, which purported termination shall not
                           be effective for purposes of this Agreement."

                  2. Effective on the Employment Agreement. All terms and
conditions of the Employment Agreement, other than as specifically amended
hereby, shall remain in full force and effect.

                  3. Counterparts. This Amendment may be executed in
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

                  IN WITNESS WHEREOF, the parties hereto have duly executed
this Amendment on the day and year first above written.

                                   HEALTHWORLD CORPORATION

                                   By:       /s/ Steven Girgenti
                                       --------------------------------
                                       Steven Girgenti, Chairman of the
                                       Board and Chief Executive Officer

                                            /s/ Stuart Diamond
                                       --------------------------------
                                                Stuart Diamond

                                      5