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                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                               Amendment No. 4 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)

                                    594941106
                      (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:  [X]

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         This Amendment No. 4 (the "Amendment"), the final 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, as previously amended and supplemented (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.

Items 1 through 9 and 11.

         Items 1 through 9 and 11 of the Schedule TO, which incorporate by
reference the information contained in the Offer to Purchase, are hereby amended
and supplemented by adding thereto the following:

         The Offer expired at 12:00 midnight, New York City time, on Monday,
July 23, 2001. Pursuant to the Offer, based upon a preliminary report from the
Depositary, the Purchaser accepted for payment 7,856,064 Shares, representing
approximately 90.611% of the outstanding Shares (including 36,248 Shares
tendered pursuant to guaranteed delivery). On July 24, 2001, Danaher issued a
press release announcing the closing of the tender offer and its intention to
acquire the remaining Shares through a cash merger, expected to be completed
shortly.

         The full text of Danaher's July 24, 2001 press release is attached as
Exhibit (a)(12) hereto and incorporated herein by reference.


Item 12. Exhibits.

         Item 12 of the Schedule TO is hereby amended by adding thereto the
following:

(a)(12)   Text of Press Release issued by Danaher on July 24, 2001.


                                    SIGNATURE

         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 24, 2001.

                                PHOENIX ACQUISITION CORP.



                                By         /s/ Christopher C. McMahon
                                         -----------------------------------
                                         Name: Christopher C. McMahon
                                         Title: Vice President and Secretary


                                DANAHER CORPORATION



                                By         /s/ Christopher C. McMahon
                                         -----------------------------------
                                         Name: Christopher C. McMahon
                                         Title: Vice President -- Controller


                                  EXHIBIT INDEX

*(a)(1)      Offer to Purchase, dated June 21, 2001.
*(a)(2)      Form of Letter of Transmittal.
*(a)(3)      Form of Notice of Guaranteed Delivery.
*(a)(4)      Form of Letter to Brokers, Dealers, Commercial Banks, Trust
             Companies and Other Nominees.
*(a)(5)      Form of Letter to Clients for use by Brokers, Dealers, Commercial
             Banks, Trust Companies and Other Nominees.
*(a)(6)      Text of press release issued by Danaher dated June 13, 2001 (filed
             with the Securities and Exchange Commission under cover of Schedule
             TO-C by Danaher on June 13, 2001 and incorporated herein by
             reference).
*(a)(7)      Text of press release issued by Fluke Networks, Inc. dated June 13,
             2001 (filed with the Securities and Exchange Commission under cover
             of Schedule TO-C by Danaher on June 13, 2001 and incorporated
             herein by reference).
*(a)(8)      Guidelines for Certification of Taxpayer Identification Number on
             Substitute Form W-9.
*(a)(9)      Form of summary advertisement dated June 21, 2001.
*(a)(10)     Text of Press Release issued by Danaher on July 20, 2001.
*(a)(11)     Text of Press Release issued by Danaher on July 23, 2001.
  (a)(12)    Text of Press Release issued by Danaher on July 24, 2001.
*(d)(1)      Agreement and Plan of Merger, dated June 12, 2001, among Danaher,
             the Purchaser and Microtest.
*(d)(2)      Confidentiality Agreement, dated February 25, 1999, between Danaher
             and Microtest, as amended May 22, 2001.
(g)          None.
(h)          Not applicable.

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*Previously filed