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                                                                     Exhibit 4.2
                                                                     -----------

                            SUPPLEMENTAL INDENTURE
                         [to December 1998 Indenture]



     Supplemental Indenture (the "Supplemental Indenture"), dated as of April 9,
1999, by and among Barricade Light & Rental, Inc., Mayer-Hammant Equipment,
L.L.C., and Wellesley Crane Service Co., Inc. (collectively, the "New Subsidiary
Guarantors"), each a direct or indirect wholly-owned subsidiary of National
Equipment Services, Inc., a Delaware corporation (the "Company"), and Harris
Trust and Savings Bank, as trustee under the indenture referred to below (the
"Trustee"). Capitalized terms used herein and not defined herein shall have the
meaning ascribed to them in the Indenture (as defined below).

                              W I T N E S S E T H

     WHEREAS, the Company has heretofore executed and delivered to the Trustee
an indenture (as supplemented, the "Indenture"), dated as of December 11, 1998,
providing for the issuance of an aggregate principal amount of $175,000,000 of
10% Senior Subordinated Notes due 2004 (the "Series C Notes");

     WHEREAS, on March 16, 1999, the Company completed its offer to exchange its
10% Senior Subordinated Notes due 2004, Series D (the "Series D Notes" and,
together with the Series C Notes, the "Senior Subordinated Notes"), which have
been registered under the Securities Act of 1933, as amended, and which were
issued under the Indenture, for all of its outstanding Series C Notes;

     WHEREAS, Sections 4.16 and 11.03 of the Indenture provide that under
certain circumstances the Company is required to cause certain of its
Subsidiaries to execute and deliver to the Trustee a supplemental indenture
pursuant to which such Subsidiaries shall unconditionally guarantee all of the
Company's Obligations under the Senior Subordinated Notes pursuant to a
Subsidiary Guarantee on the terms and conditions set forth herein; and

     WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee is
authorized to execute and deliver this Supplemental Indenture.

     NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the New
Subsidiary Guarantors and the Trustee mutually covenant and agree for the equal
and ratable benefit of the Holders of the Senior Subordinated Notes as follows:

     1.   Capitalized Terms. Capitalized terms used herein without definition
shall have the meanings assigned to them in the Indenture.

     2.   Agreement to Subsidiary Guarantee. The New Subsidiary Guarantors
hereby agree, jointly and severally with all other Subsidiary Guarantors, to
guarantee the Company's Obligations under the Senior Subordinated Notes and the
Indenture on the terms and subject to the
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conditions set forth in Article 11 of the Indenture and to be bound by all other
applicable provisions of the Indenture.

     3.   No Recourse Against Others. No past, present or future director,
officer, employee, incorporator, shareholder, equityholder or agent of any
Subsidiary Guarantor, as such, shall have any liability for any obligations of
the Company or any Subsidiary Guarantor under the Senior Subordinated Notes, any
Subsidiary Guarantees, the Indenture or this Supplemental Indenture or for any
claim based on, in respect of, or by reason of, such obligations or their
creation. Each Holder by accepting a Senior Subordinated Note waives and
releases all such liability. The waiver and release are part of the
consideration for issuance of the Senior Subordinated Notes.

     4.   New York Law to Govern. The internal law of the State of New York
shall govern and be used to construe this Supplemental Indenture.

     5.   Counterparts. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement.

     6.   Effect of Headings. The section headings herein are for convenience
only and shall not affect the construction hereof.

     7.   The Trustee. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Indenture or for or in respect of the correctness of the recitals of fact
contained herein, all of which recitals are made solely by the New Subsidiary
Guarantors.

                                 *    *    *
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     IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed, all as of the date first above written.

                                   BARRICADE LIGHT & RENTAL, INC.

                                   By: /s/ Paul R. Ingersoll
                                      -----------------------------------
                                      Name: Paul R. Ingersoll
                                      Title: Vice President and Secretary


                                   MAYER-HAMMANT EQUIPMENT, L.L.C.

                                   By: /s/ Paul R. Ingersoll
                                      -----------------------------------
                                      Name: Paul R. Ingersoll
                                      Title: Vice President and Secretary


                                   WELLESLEY CRANE SERVICE CO., INC.

                                   By: /s/ Paul R. Ingersoll
                                      -----------------------------------
                                      Name: Paul R. Ingersoll
                                      Title: Vice President and Secretary


                                   HARRIS TRUST AND SAVINGS BANK, AS TRUSTEE

                                   By: /s/ C. Potter
                                      ------------------------------
                                      Name:
                                      Title: