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                                                                     EXHIBIT 4.2

                       AMENDMENT NO. 1 TO RIGHTS AGREEMENT

     This Amendment No. 1 to Rights Agreement, dated as of January 112001 (this
"Amendment"), is by and between Dynamex Inc., a Delaware corporation (the
"Company"), and ComputerShare Investor Services, LLC (formerly Harris Trust and
Savings Bank) (the "Rights Agent").

     WHEREAS, the Company and the Rights Agent have entered into a Rights
Agreement (the "Rights Agreement"), dated as of July 5, 1996 (capitalized terms
not otherwise defined herein shall have the respective meanings set forth in the
Rights Agreement; and

     WHEREAS, the Company desires to amend the Rights Agreement and, pursuant to
Section 27 of the Rights Agreement, hereby directs the Rights Agent to join in
this Amendment;

     NOW, THEREFORE, in consideration of the premises and the mutual agreements
herein set forth, the parties hereto hereby agree as follows:

     1. Section 1(a) of the Rights Agreement shall be amended hereinafter to
read as follows:

          (a) "Acquiring Person" shall mean any Person who or which, together
     with all Affiliates and Associates of such Person, shall be the Beneficial
     Owner of 15% or more of the shares of Common Stock of the Company then
     outstanding, but shall not include (i) the Company, (ii) any Subsidiary of
     the Company and (iii) any employee benefit plan of the Company or of any
     Subsidiary of the Company or any entity holding such shares of Common Stock
     for or pursuant to the terms of any such plan. Notwithstanding the
     foregoing, no Person shall become an "Acquiring Person" as the result of an
     acquisition by the Company of its shares of Common Stock which, by reason
     of reducing the number of such shares of Common Stock outstanding,
     increases the number of shares of Common Stock Beneficially Owned by such
     Person to 15% or more of such shares of Common Stock then outstanding;
     provided, however, that if any Person, other than a Person excepted in the
     first sentence of this definition, shall become the Beneficial Owner of 15%
     or more of such outstanding shares of Common Stock by reason of any
     purchase by the Company of its shares of Common Stock and shall, after such
     purchase, become the Beneficial Owner of any additional such shares of
     Common Stock, then such Person shall be deemed to be an "Acquiring Person".

     2. Section 3(c) of the Rights Agreement shall be amended hereinafter to
read as follows:

          "(c) Certificates for shares of Common Stock of the Company which
     become outstanding (including, without limitation, shares of Common Stock
     referred to in the last sentence of this subsection (c) which shall be
     subsequently reissued) after the Record Date and prior to the earliest of
     the Distribution Date, the Redemption Date and the Final Expiration Date
     shall also be deemed to constitute certificates for the Rights, but shall

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     have impressed, printed or written thereon, or otherwise affixed thereto, a
     legend in substantially the following form:

               This certificate also evidences and entitles the holder hereof to
          certain Rights as set forth in the Rights Agreement, dated as of July
          5, 1996 and as amended to date (the "Rights Agreement"), between
          Dynamex Inc. and ComputerShare Investor Services, LLC, the terms of
          which are incorporated herein by reference and a copy of which is on
          file at the principal executive office of Dynamex Inc. Under certain
          circumstances, as set forth in the Rights Agreement, such Rights will
          be evidenced by separate certificates and will no longer be evidenced
          by this certificate. Dynamex Inc. will mail to the holder of this
          certificate a copy of the Rights Agreement without charge after
          receipt of a written request therefor. Under certain circumstances
          described in the Rights Agreement, Rights issued to or held by any
          Person who is, was or becomes an Acquiring Person or an Affiliate or
          Associate thereof (as such terms are defined in the Rights Agreement),
          whether currently held by or on behalf of such Person or any
          subsequent holder, may become null and void.

     Certificates containing the foregoing legend, until the Distribution Date
     or the earlier of the Redemption Date and the Final Expiration Date, shall
     also be deemed to constitute certificates for the Rights associated with
     the shares of Common Stock represented by such certificates, and the
     surrender for transfer of any such certificate shall also constitute the
     transfer of the Rights associated with the shares of Common Stock
     represented thereby. In the event that the Company shall purchase or
     acquire any of its shares of Common Stock after the Record Date but prior
     to the Distribution Date, any Rights associated with such shares of Common
     Stock shall be deemed cancelled and retired so that the Company shall not
     be entitled to exercise any Rights associated with shares of Common Stock
     which are no longer outstanding."

     3. Section 21 of the Rights Agreement shall be amended hereinafter to read
as follows:

          "SECTION 21. CHANGE OF THE RIGHTS AGENT. The Rights Agent or any
     successor Rights Agent may resign and be discharged from its duties under
     this Agreement upon 30 days' prior notice mailed to the Company. The
     Company may remove the Rights Agent or any successor Rights Agent upon 30
     days' prior notice mailed to the Rights Agent or successor Rights Agent, as
     the case may be, and to each transfer agent of the Common Stock and
     Preferred Stock by registered or certified mail, postage prepaid, and to
     each registered holder of the Rights Certificates by first-class mail,
     postage prepaid. If the Rights Agent shall resign or be removed or shall
     otherwise become incapable of acting, the Company shall appoint a successor
     Rights Agent. If the Company shall fail to make such appointment within 30
     days after giving notice of such removal or after receiving notice of such
     resignation or incapacity either from the resigning or incapacitated Rights

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     Agent or from the registered holder of a Rights Certificate (who shall,
     with such notice, submit his Rights Certificate for inspection by the
     Company), then the Rights Agent or the registered holder of any Rights
     Certificate may apply to any court of competent jurisdiction for the
     appointment of a successor Rights Agent. Any successor Rights Agent,
     whether appointed by the Company or by such a court, shall be (a) a
     corporation or trust company (or similar form of entity under the laws of
     any state of the United States or a foreign jurisdiction) authorized to
     conduct business under the laws of the United States or any state of the
     United States, which is authorized under such laws to exercise corporate
     trust, fiduciary or stockholder services powers and is subject to
     supervision or examination by federal or state authority and which has at
     the time of its appointment as Rights Agent a combined capital and surplus
     of at least $10,000,000 or (b) an Affiliate controlled by a corporation
     described in clause (a) of this sentence. After its appointment, the
     successor Rights Agent shall be vested with the same powers, rights, duties
     and responsibilities as if it had been originally named as Rights Agent
     without further act or deed; but the predecessor Rights Agent shall deliver
     and transfer to the successor Rights Agent any property at the time held by
     it hereunder, and execute and deliver any further assurance, conveyance,
     act or deed necessary for the purpose. Not later than the effective date of
     any such appointment, the Company shall file notice thereof in writing with
     the predecessor Rights Agent and each transfer agent of the Common Stock
     and Preferred Stock, and mail notice thereof to the registered holders of
     the Rights Certificates. Failure to give any notice provided for in this
     Section 21, however, or any defect therein, shall not affect the legality
     or validity of the resignation or removal of the Rights Agent or the
     appointment of any successor Rights Agent."

     4. Except as provided above, the Rights Agreement shall continue unmodified
and in full force and effect.

     5. This Amendment shall be deemed to be a contract made under the laws of
the State of Delaware and for all purposes shall be governed by and construed in
accordance with the laws of such State applicable to contracts to be made and
performed entirely within such State.

     6. This Amendment may be executed in any number of counterparts, each of
which shall for all purposes be deemed to be an original, but all such
counterparts shall together constitute one and the same instrument.

                         [signatures on following page]

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     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and their respective corporate seals to be affixed and attested,
all as of the day and year first above written.

                                       DYNAMEX INC.

                                       By: /s/ Richard K. McClelland
                                           -------------------------------------
(Corporate Seal)                           Name: Richard K. McClelland
                                                 President

Attest:

By: /s/  Jeffrey N. MacDowell
    -------------------------------
Name: Jeffrey N. MacDowell
Title: VP-Finance and Asst. Secretary

                                       COMPUTERSHARE INVESTOR SERVICES, LLC
                                         AS RIGHTS AGENT

                                       By: /s/ Rozlynn R. Orr
                                           -------------------------------------
(Corporate Seal)                           Name: Rozlynn R. Orr
                                                 Relationship Manager

Attest:

By: /s/   Mark Asbury
    -------------------------------
Name: Mark Asbury
Title: Vice President

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