EXHIBIT 4.2

                            SUPPLEMENTAL INDENTURE


     THIS SUPPLEMENTAL INDENTURE, dated as of May 19, 1998, among Advanstar
Communications Inc., a New York corporation (the "Company"), Applied Business
teleCommunications, a California corporation and a wholly-owned subsidiary of
the Company (the "New Subsidiary Guarantor"), and The Bank of New York (the
"Trustee").

     WHEREAS, the Company, the Guarantors listed therein and the Trustee entered
into an Indenture dated as of April 30, 1998 (together with this Supplemental
Indenture, the "Indenture") to provide, among other things, for the
authentication, delivery and administration of the Company's 9 1/4% Senior
Subordinated Notes due 2008 (the "Notes") which evidence certain indebtedness of
the Company;

     WHEREAS, pursuant to a Stock Purchase Agreement dated as of May 7, 1998 by
and among the Company, the New Subsidiary Guarantor, Patrick S. Portway and
Shawn Portway, the Company acquired all of the outstanding capital stock of the
New Subsidiary Guarantor; and

     WHEREAS, pursuant to Section 3.12 of the Indenture, the Company has agreed,
and agreed to cause each Restricted Subsidiary after created or acquired, to
enter into a supplemental indenture pursuant to which such Restricted Subsidiary
will become a party to the Indenture and thereby unconditionally Guarantee, on a
joint and several basis, the full and prompt payment of the principal of,
premium, if any and interest on the Securities on a senior subordinated basis.

     NOW, THEREFORE, the Company, the Subsidiary Guarantor and the Trustee agree
as follows:

     1.  Defined Terms.  All capitalized terms not defined herein shall have the
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meaning as set forth in the Indenture.

     2.  Amendment of Indenture.  The Company, the New Subsidiary Guarantor and
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the Trustee hereby agree that the Indenture shall be amended by this
Supplemental Indenture to include the New Subsidiary Guarantor as a party
thereto and that, for purposes of the Indenture, the New Subsidiary Guarantor
shall be a Restricted Subsidiary and a Subsidiary Guarantor. The New Subsidiary
Guarantor hereby agrees to bound by the Indenture as a Subsidiary Guarantor for
all purposes as if the New Subsidiary Guarantor were a party to the original
Indenture, including, without limitation, to Guarantee unconditionally, on a
joint and several basis, the full and prompt payment of the principal of,
premium, if any and interest on the Securities on a senior subordinated basis.

     3.  Continuation of Provisions.  Except as amended hereby, all of the terms
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and conditions of the Indenture shall continue in full force and effect and are
hereby in all respects ratified and confirmed.

 
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     4.  GOVERNING LAW.  THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY, AND
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CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK BUT WITHOUT
GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT
THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

     5.  COUNTERPARTS.  This Supplemental Indenture may be executed in any
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number of counterparts, each of which shall be an original; but such
counterparts shall together constitute but one and the same instrument.

     6.  HEADINGS.  The headings of the Sections of this Supplemental Indenture
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have been inserted for convenience of reference only, are not to be considered a
part hereof and shall not modify or restrict any of the terms or provisions
hereof.

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     IN WITNESS WHEREOF, each party hereto has caused this Supplemental
Indenture to be duly executed, all as of the date first written above.


                         ADVANSTAR COMMUNICATIONS INC.


                         By: /s/ Robert L. Krakoff 
                             _______________________________
                         Name: Robert L. Krakoff
                         Title: Chairman & Chief Executive Officer



                         APPLIED BUSINESS TELECOMMUNICATIONS


                         By: /s/ Robert L. Krakoff 
                             _______________________________
                         Name: Robert L. Krakoff
                         Title: President



                         THE BANK OF NEW YORK
                         as Trustee


                         By: /s/ Mary Jane Schmalzel
                             _______________________________
                         Name: Mary Jane Schmalzel
                         Title: Chairman & Chief Executive Officer