Washington, D.C. 20549

                              Amendment No. 1 to
                                  Schedule TO
                     Tender Offer Statement under Section
          14(d)(1) or 13(e)(1) of the Securities Exchange Act of 1934

                                Microtest, Inc.
                           (Name of Subject Company)

                           Phoenix Acquisition Corp.
                              Danaher Corporation
                        (Name of Filing Person-Offeror)

                   Common Stock, Par Value $0.001 Per Share
                        Preferred Share Purchase Rights
                        (Title of Class of Securities)

                     (CUSIP Number of Class of Securities)

                              Patrick W. Allender
                           Executive Vice President,
                     Chief Financial Officer and Secretary
                   2099 Pennsylvania Avenue, NW, 12th Floor
                          Washington, D.C. 20006-1813
                           Telephone: (202) 828-0850
           (Name, Address and Telephone Number of Person Authorized
      to Receive Notices and Communications on Behalf of Filing Persons)

                                   Copy to:

                             Mark A. Dewire, Esq.
                          Wilmer, Cutler & Pickering
                               2445 M Street, NW
                         Washington, D.C.  20037-1420
                           Telephone: (202) 663-6000

[ ]  Check the box if the filing relates solely to preliminary communications
     made before the commencement of a tender offer.

     Check the appropriate boxes below to designate any transactions to which
     the statement relates:

[X]  third-party tender offer subject to Rule 14d-1.
[ ]  issuer tender offer subject to Rule 13e-4.
[ ]  going-private transaction subject to Rule 13e-3.
[ ]  amendment to Schedule 13D under Rule l3d-2.

     Check the following box if the filing is a final amendment reporting the
     results of the tender offer:  [  ]


     This Amendment No. 1 (the "Amendment") amends and supplements the Tender
Offer Statement on Schedule TO filed by Danaher Corporation, a Delaware
corporation ("Danaher"), and Phoenix Acquisition Corp., a Delaware corporation
and an indirect, wholly-owned subsidiary of Danaher (the "Purchaser"), on June
21, 2001 (the "Schedule TO"), relating to the offer by the Purchaser to purchase
all outstanding shares of common stock, par value $0.001 per share (the
"Shares"), of Microtest, Inc., a Delaware corporation ("Microtest") at $8.15 per
Share, net to the seller in cash, upon the terms and subject to the conditions
set forth in the Offer to Purchase, dated June 21, 2001 (the "Offer to
Purchase") and in the related Letter of Transmittal, copies of which are
attached as Exhibits (a)(1) and (a)(2), respectively, to the Schedule TO.

     All capitalized terms used in this Amendment without definition have the
meanings attributed to them in the Schedule TO.

     The Items of the Schedule TO set forth below are hereby supplemented and,
as so supplemented, amended as follows:

Item 11.    Additional Information

     Item 11 of the Schedule TO, which incorporates by reference the information
contained in the Offer to Purchase, is hereby amended by:

     .    restating the first sentence of the third to last paragraph of Section
          14 of the Offer to Purchase in full as follows:

     "The foregoing conditions (including those set forth in clauses (A), (B)
and (C) of the initial paragraph of this Section 14) are for the benefit of
Danaher and the Purchaser and may be asserted by Danaher or the Purchaser
regardless of the circumstances giving rise to any such conditions, and may be
waived by Danaher or the Purchaser in whole or in part at any time and from time
to time (provided that no individual condition may be reasserted after it has
been waived, and provided further that, except for the conditions set forth in
clause (B) of the initial paragraph, no condition may be asserted or waived
after the Expiration Date) in each case in the exercise of the reasonable
discretion of Danaher and the Purchaser and subject to the terms of the Merger
Agreement."; and

     .    adding to the end of the fifth paragraph of Section 15 of the Offer to
          Purchase the following sentence:

     "The required waiting period with respect to the Offer and the Merger under
the HSR Act expired at 11:59 p.m., New York City time, on July 3, 2001."


     After due inquiry and to the best of my knowledge and belief, I certify
that the information set forth in this statement is true, complete and correct.

Dated: July 3, 2001.
                                    PHOENIX ACQUISITION CORP.

                                    By     /s/ Daniel L. Comas
                                         Name: Daniel L. Comas
                                         Title: Vice President

                                    DANAHER CORPORATION

                                    By  /s/ Patrick W. Allender
                                         Name: Patrick W. Allender
                                         Title: Executive Vice President,
                                         Chief Financial Officer and Secretary