STOCKHOLDERS SUPPORT AGREEMENT

          STOCKHOLDERS SUPPORT AGREEMENT dated as of April 21, 1999, by and 
among DANAHER CORPORATION, a Delaware corporation ("Parent"), on the one 
hand, and each of KATHRYN C. HACH-DARROW and BRUCE J. HACH (each a 
"Stockholder" and, collectively, the "Stockholders"), on the other hand.  
Each Stockholder is executing this Agreement in her or his capacity as a 
stockholder of HACH COMPANY, a Delaware corporation (the "Company").

          WHEREAS, Parent, H20 ACQUISITION CORP., a Delaware corporation and 
a wholly owned subsidiary of Parent ("Sub"), and the Company, are entering 
into an Agreement and Plan of Merger (the "Merger Agreement"; capitalized 
terms used without definition herein having the meanings ascribed thereto in 
the Merger Agreement) under which the Stockholders will receive substantial 
value for their interest in the Company;

          WHEREAS, a significant portion of the goodwill and value of the 
Company resides in the "Hach" tradename;

          WHEREAS, each Stockholder is a director of the Company, who 
possesses significant knowledge and information about and expertise in the 
Company Business (as defined below) which is extremely valuable to 
competitors of the Company, and accordingly Parent has required as a 
condition to its willingness to enter into the Merger Agreement that each 
Stockholder make, and each Stockholder has agreed to make, the commitments 
set forth herein; 

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

          Section 1.     AGREEMENT TO SUPPORT TRANSACTION.  Until the earlier 
of the Effective Time and the termination of this Agreement in accordance 
with its terms: 

          (a)  Each Stockholder hereby agrees that, immediately following the 
execution and delivery of this Agreement and the Merger Agreement, she or he 
shall execute and deliver, or cause to be executed and delivered by the 
record owner of shares beneficially owned by such Stockholder, in accordance 
with Section 228 of the DGCL, the Restated Certificate of Incorporation and 
By-laws of the Company, the Written Consent of Stockholders Without a 
Meeting, in the form attached hereto as Annex A, with respect to all shares 
of Company Common Stock that are owned beneficially or of record by such 
Stockholder or as to which such Stockholder has, directly or indirectly, the 
right to vote or direct the voting. 

          (b)  Each Stockholder hereby further agrees she or he shall, from 
time to time, at the request of Parent, (i) timely execute and deliver (or 
cause to be timely executed and delivered) an additional written consent with 
respect to, or (ii) vote, or cause to be voted, at any meeting of 
stockholders of the Company held prior to the earlier of the Effective Time 
and the termination of this Agreement or at any adjournment or postponement 
thereof, in person or by proxy, all shares of Company Common Stock, and any 
other voting securities of the Company (whether acquired heretofore or 
hereafter), that are beneficially owned by such Stockholder or her 




or his Affiliates or as to which such Stockholder or any of her or his 
Affiliates has, directly or indirectly, the right to vote or direct the 
voting, in favor of approval and adoption of the Merger Agreement and the 
Merger (including as they may be amended by the Board of Directors of the 
Company), and any action required in furtherance thereof and against any 
action or agreement that would result in a material breach of any 
representation, warranty, covenant or obligation of the Company contained in 
the Merger Agreement. 

          (c)  Other than pursuant to the Merger or with Parent's prior 
written consent, each Stockholder agrees that she or he will not, and will 
not permit any company, trust or other entity controlled by such Stockholder 
to, and will not permit any of such Stockholder's Affiliates to, contract to 
sell, sell, pledge, encumber or otherwise transfer or dispose of any Company 
Common Stock beneficially owned by her or him or any interest therein or 
securities convertible thereinto or any voting rights with respect thereto 
without giving Parent prior written notice thereof and in any event if such 
transaction could reasonably be expected to jeopardize Parent's ability to 
account for the Merger as a "pooling of interests."

          (d)  Each Stockholder hereby revokes any and all previous proxies 
with respect to such Stockholder's shares of Company Common Stock or any 
other voting securities of the Company.

          (e)  Each Stockholder hereby agrees to, will cause any company, 
trust or other entity controlled by such Stockholder to, and will cause such 
Stockholder's Affiliates to, cooperate fully with Parent in connection with 
the Merger Agreement and the transactions contemplated thereby.  Each 
Stockholder agrees that neither such Stockholder nor any of her or his 
representatives, agents or Affiliates will, directly or indirectly, 
encourage, solicit or engage in discussions or negotiations with any third 
party (other than Parent) concerning any merger, consolidation, business 
combination, sale of a significant amount of securities or assets or similar 
transaction ("Alternative Transactions") other than the transactions 
contemplated hereby and by the Merger Agreement.  Each Stockholder shall 
immediately request that any Person that has received directly or indirectly 
from such Stockholder any confidential information involving the Company or 
any of its Subsidiaries return all copies thereof to the Company and shall, 
and shall cause her or his representatives, agents and Affiliates to, 
terminate all discussions or negotiations with any Person with respect to any 
Alternative Transaction.  Each Stockholder will notify Parent immediately of 
any inquiries or proposals with respect to any such transaction that are 
received by, or any such negotiations or discussions of which such 
Stockholder is aware that are sought to be initiated with, such Stockholder 
or any of such Stockholder's Affiliates or the Company or any of its 
Subsidiaries, will advise Parent of the identity of any Person proposing any 
such Alternative Transaction and of the terms thereof and shall keep Parent 
apprised with respect to all matters relating thereto.  

          (f)  Each  Stockholder is signing this Agreement solely in her or 
his capacity as a record holder and beneficial owner of shares of Company 
Common Stock and nothing herein shall limit or affect any actions taken by a 
Stockholder in her or his capacity as an officer or director of the Company, 
subject to the provisions of the Merger Agreement.


                                      2




          Section 2.     RULE 145; POOLING LETTER.  Each Stockholder is on 
the date hereof executing, and shall cause each of such Stockholder's 
Affiliates identified as Affiliates of the Company on the Company's letter 
referred to in Section 5.10 of the Merger Agreement to execute by the 
thirtieth day prior to the Effective Time, a written agreement in the form 
attached as Exhibit 5.10 to the Merger Agreement (relating to compliance with 
Rule 145 and pooling rules).

          Section 3.     TAX REPRESENTATIONS.  Each Stockholder shall deliver 
to Parent's counsel and the Company's counsel, if so requested by such 
counsel, respectively, a certificate setting forth such representations as 
are customary to be given by shareholders in transactions such as the Merger 
in connection with the opinions contemplated by Sections 6.2(d) and 6.3(c) of 
the Merger Agreement.

          Section 4.     COVENANT NOT TO COMPETE.  (a)  Each Stockholder 
agrees that, commencing at the Effective Time and continuing until the third 
anniversary of the Effective Time, such Stockholder shall not carry on or 
participate in the design, manufacture or marketing of laboratory 
instruments, process analyzers and test kits for analyzing the properties of 
water and other aqueous solutions (any such activities being referred to 
herein as "Company Business") or in any business in competition with any 
Company Business, as conducted by the Company on the date hereof, in any 
country in which the Company operates. Each Stockholder shall not, whether or 
not for compensation, engage in any Company Business, or assist or advise any 
other Person in such Person's conduct of any Company Business, whether as a 
director, officer, employee, consultant, adviser, independent contractor or 
otherwise; PROVIDED, HOWEVER, that the Stockholders shall not be prohibited 
from owning up to five percent (5%) of the outstanding securities in any 
Person that is engaged in any Company Business as a passive investor. 

          (b)       Each Stockholder agrees that, commencing at the Effective 
Time and continuing until the fifth anniversary of the Effective Time, such 
Stockholder shall not (i) lend or allow such Stockholder's name or reputation 
to be used in or to promote any Company Business, other than for the benefit 
of Parent and its Affiliates (including the Company); or (ii) solicit, divert 
or attempt to divert from Parent and its Affiliates any business 
constituting, or any customer of, or any supplier of, any part of the Company 
Business then conducted by the Company, Parent or any of their Affiliates.

          Section 5.     COVENANT NOT TO SOLICIT.  In addition to the 
foregoing, each Stockholder further agrees that such Stockholder shall not, 
commencing at the Effective Time and continuing until the fifth anniversary 
of the Effective Time, induce or attempt to induce any Person (i) engaged or 
employed currently or within the prior 12 months (whether part-time or 
full-time) by the Company or any of its Affiliates to leave the employ of or 
engagement with the Company, or its Affiliates, as the case may be, or to 
cease providing the services to or on behalf of the Company or its 
Affiliates, as the case may be, then provided by such Person, or in any other 
manner seek to engage, employ or contract for the services of, any such 
Person (whether or not for compensation) in any capacity, or (ii) that is 
then or has been within the prior 12 months a customer or supplier with 
respect to any Company Business to interfere, in any way, directly or 
indirectly, with the business relationship between the Company or any of its 
Affiliates and any such customer.


                                      3



          Section 6.     REPRESENTATIONS AS TO STOCK OWNERSHIP.  Each 
Stockholder represents and warrants to Parent that (a) Schedule I hereto sets 
forth, opposite such Stockholder's name, the number and type of shares of 
Company Common Stock or other securities of the Company of which such 
Stockholder is the record or beneficial owner, and (b) such Stockholder is 
the lawful owner of such shares, free and clear of all liens, charges, 
encumbrances, voting agreements and commitments of every kind, except as may 
be disclosed on Schedule I. 

          Section 7.     EFFECTIVENESS AND TERMINATION.  In the event the 
Merger Agreement is terminated in accordance with its terms, this Agreement 
shall automatically terminate and be of no further force or effect. Upon such 
termination, except for any rights any party may have in respect of any 
breach by any other party of its obligations hereunder, none of the parties 
hereto shall have any further obligation or liability hereunder.

          Section 8.     MISCELLANEOUS.

          (a)  NOTICES, ETC.  All notices, requests, demands or other 
communications required by or otherwise with respect to this Agreement shall 
be in writing and shall be deemed to have been duly given when delivered 
personally (by courier service or otherwise) or when delivered by telecopy 
(with receipt acknowledged), to Parent at Danaher Corporation, 1250 24th 
Street, N.W., Washington, D.C. 20037, or to any Stockholder at her or his 
address set forth in the records of the Company, or to such other address as 
any such party shall have designated by notice so given to each other party.

          (b)  AMENDMENTS, WAIVERS, ETC.  This Agreement may not be amended, 
changed, supplemented, waived or otherwise modified or terminated except by 
an instrument in writing signed by each party hereto. The failure of any 
party hereto to exercise any right, power or remedy provided under this 
Agreement or otherwise available in respect hereof at law or in equity, or to 
insist upon compliance by any other party hereto with its obligations 
hereunder, and any custom or practice of the parties at variance with the 
terms hereof, shall not constitute a waiver by such party of its right to 
exercise any such or other right, power or remedy or to demand such 
compliance.

          (c)  SUCCESSORS AND ASSIGNS.  This Agreement shall be binding upon 
and shall inure to the benefit of and be enforceable by the parties and their 
respective successors and assigns.  Any transfer of shares of Company Common 
Stock notwithstanding, the transferor shall remain liable for the performance 
of all obligations under this Agreement of transferor.  Any transferee of 
shares of Company Common Stock permitted pursuant to this Agreement shall 
take such shares subject to the provisions of this Agreement and deliver to 
Parent in advance of such transfer its signed acknowledgment to such effect.

          (d)  ENTIRE AGREEMENT.  This Agreement (together with the Merger 
Agreement and the other agreements and documents expressly contemplated 
hereby and thereby) embodies the entire agreement and understanding among the 
parties relating to the subject matter hereof and supersedes all prior 
agreements and understandings relating to such subject matter.  There are no 
representations, warranties or covenants by the parties hereto relating to 
such subject matter other than those expressly set forth in this Agreement 
and the Merger Agreement.


                                      4



          (e)  SEVERABILITY.  If any term of this Agreement or the 
application thereof to any party or circumstance shall be held invalid or 
unenforceable to any extent, the remainder of this Agreement and the 
application of such term to the other parties or circumstances shall not be 
affected thereby and shall be enforced to the greatest extent permitted by 
applicable law, PROVIDED that, in such event, the parties shall negotiate in 
good faith in an attempt to agree to another provision (in lieu of the term 
or application held to be invalid or unenforceable) that will be valid and 
enforceable and will carry out to the maximum extent possible the parties' 
intentions hereunder.  

          (f)  REMEDIES.  The parties acknowledge that money damages are not 
an adequate remedy for violations of this Agreement and that any party may, 
in its sole discretion, apply to a court of competent jurisdiction for 
specific performance or injunctive or such other relief as such court may 
deem just and proper in order to enforce this Agreement or prevent any 
violation hereof and, to the extent permitted by applicable law, each party 
waives any objection to the imposition of such relief or any requirement for 
a bond.  All rights, powers and remedies provided under this Agreement or 
otherwise available in respect hereof at law or in equity shall be cumulative 
and not alternative, and the exercise or beginning of the exercise of any 
thereof by any party shall not preclude the simultaneous or later exercise of 
any other such right, power or remedy by such party.

          (g)  GOVERNING LAW; JURISDICTION. This Agreement and all disputes 
hereunder shall be governed by and construed and enforced in accordance with 
the internal laws of the State of Delaware, without regard to principles of 
conflicts of law.  Each party hereby irrevocably submits to the exclusive 
jurisdiction of the Court of Chancery in the State of Delaware or the United 
States District Court of Delaware in any action, suit or proceeding arising 
in connection with this Agreement, and agrees that any such action, suit or 
proceeding shall be brought only in such court (and waives any objection 
based on FORUM NON CONVENIENS or any other objection to venue therein). Each 
party hereto hereby waives any right to a trial by jury in connection with 
any such action, suit or proceeding.  

          (h)  NAME, CAPTIONS, GENDER.  The name assigned this Agreement and 
the section captions used herein are for convenience of reference only and 
shall not affect the interpretation or construction hereof.  Whenever the 
context may require, any pronoun used herein shall include the corresponding 
masculine, feminine or neuter forms.

          (i)  COUNTERPARTS.  This Agreement may be executed in any number of 
counterparts, each of which shall be deemed to be an original, but all of 
which together shall constitute one instrument.  Each counterpart may consist 
of a number of copies each signed by less than all, but together signed by 
all, the parties hereto.


                                      5



          IN WITNESS WHEREOF, the parties have duly executed this Agreement 
as of the date first above written.

                                   DANAHER CORPORATION

                                   By:  /s/ Patrick W. Allender 
                                        -----------------------------------
                                        Name:     Patrick W. Allender 
                                        Title:    Senior Vice President and
                                                  Chief Financial Officer

                                   STOCKHOLDERS


                                    /s/ Kathryn Hach-Darrow 
                                    ------------------------------
                                    Name:  Kathryn Hach-Darrow


                                    /s/ Bruce J. Hach 
                                    ------------------------------
                                    Name:  Bruce J. Hach





                                     SCHEDULE I
                                          
                                  SHARE OWNERSHIP




 NAME OF SHAREHOLDER                                    SHARES OWNED
                                         SHARES                             OPTIONS
                                                 Class A                               Class A 
                               Common Stock    Common Stock         Common Stock     Common Stock
                               ------------    ------------         ------------     ------------
                                                                          
 Kathryn C. Hach-Darrow          4,546,990      4,541,647                    0                0

 Bruce J. Hach                     238,350        227,514               20,000           54,000
                                 ---------      ---------               ------           ------
                                 ---------      ---------               ------           ------
      Total:                     4,785,340      4,769,161               20,000           54,000