EXHIBIT 10(m)
                                                                 CONFORMED COPY
                          STOCKHOLDER AGREEMENT

          AGREEMENT dated as of January 21, 1998 (the "Agreement"), by and 
among Hach Company, a Delaware corporation ("Buyer"), and Harry Stephenson, 
("Stockholder").

          WHEREAS, Buyer, Hach Acquisition Corp. ("Mergerco") and 
Environmental Test Systems, Inc. (the "Company" or "ETS") have concurrently 
herewith entered into an Agreement and Plan of Merger dated as of January 21, 
1998 (as it may be amended from time to time, the "Merger Agreement") 
pursuant to which the Company will, at the Effective Time, be merged with and 
into Mergerco a direct, wholly owned subsidiary of Buyer;

          WHEREAS, the Stockholder is the holder of the majority of the 
outstanding shares of common stock of the Company and desires that the 
Company enter into the Merger Agreement;

          WHEREAS, in furtherance of the purposes of the Merger Agreement and 
as a condition to the willingness of Buyer and Mergerco to enter into the 
Merger Agreement, the parties hereto intend to take certain actions related 
to the Merger Agreement; and

          WHEREAS, capitalized terms used herein without definition shall 
have the meanings assigned to them in the Merger Agreement.

          NOW, THEREFORE, in consideration of the foregoing and the mutual 
covenants and agreements herein contained, and intending to be legally bound 
hereby, the parties hereto hereby agree as follows:

                                   ARTICLE I
                                          
                               IRREVOCABLE PROXY
                                          
          1.1  GRANT OF IRREVOCABLE PROXY.  (a) Solely for the purpose of 
securing the approval and adoption by the stockholders of the Company of the 
Merger Agreement and the consummation of the transactions contemplated 
thereby and to prevent any action including, without limitation, any other 
merger, consolidation, sale of substantially all of the assets, 
reorganization or recapitalization, liquidation or winding up of the Company 
or any other extraordinary transaction involving the Company or any other 
corporate action the consummation of which would, directly or indirectly, in 
any way frustrate the purposes of, or prevent or delay the consummation of, 
the transactions contemplated by this Agreement or the Merger Agreement (i) 
all rights and powers of the Stockholder with respect to his shares of ETS 
Class B Stock that he may acquire (collectively the "Proxy Shares"), to vote, 
give approvals, consent, call meetings, give, receive and waive notices of 
meetings, grant proxies to others and (ii) all other voting, approval, 
consent, waiver or similar rights and powers which the Stockholder possesses 
or may in the future possess as beneficial owner of the Proxy Shares, in such 
manner as the Buyer may, in its sole discretion, deem appropriate or 
desirable solely in order to accomplish such purpose; 



provided, however, that the Stockholder hereby retains all other voting and 
other rights with respect to the Proxy Shares, including without limitation, 
the power to vote to elect or remove directors of ETS.  By giving this proxy 
the Stockholder hereby revokes any other proxy granted by him to vote any of 
the Proxy Shares.  The power and authority hereby conferred shall not be 
terminated by any act of the Stockholder or by operation of law, by lack of 
appropriate power or authority, or by the occurrence of any other event or 
events except the termination of the Merger Agreement in accordance with its 
terms and shall be binding upon all its beneficiaries, distributees, 
successors, assigns and legal representatives.

               (b)  This proxy is irrevocable, is coupled with an interest, 
is granted in consideration of Buyer's entering into the Merger Agreement and 
does not constitute any transfer of shares of ETS Class B Common Stock. This 
proxy shall terminate upon termination of the Merger Agreement in accordance 
with its terms.

               (c)  The Stockholder shall not take any action to sell or 
pledge or agree to sell or pledge any Proxy Shares to any Person (as defined 
below) other than Buyer or to grant another proxy to any Person, to solicit, 
initiate or encourage, or to vote any Proxy Shares in favor of the approval 
of any merger, consolidation, sale of substantially all of the assets, 
reorganization or recapitalization, liquidation or winding up of the Company 
or any other extraordinary transaction involving the Company, or any other 
corporate action the consummation of which would directly or indirectly, in 
any way frustrate the purposes of, or prevent or delay the consummation of 
the transactions contemplated by this Agreement and the Merger Agreement. The 
Obligations of Stockholder under this paragraph shall terminate upon 
termination of the Merger Agreement in accordance with its terms. For the 
purposes of this Agreement, "Person" shall mean an individual, partnership, 
corporation (including a business trust), joint stock company, trust, 
unincorporated association, joint venture or other entity, or a government or 
any political subdivision or agency thereof.

               (d)  If the proxy granted in Section 1.1(a) is invalid or is 
ineffective for any reason, the Stockholder hereby irrevocably agrees to vote 
in favor of the Merger Agreement at any meeting or meetings or in connection 
with any action by consent of the stockholders of the Company.

          1.2  ACTIONS WITH RESPECT TO AFFILIATES.  The Stockholder agrees to 
use his reasonable efforts to cause the Company to perform all obligations 
and agreements and comply with all covenants and satisfy all conditions 
required by the Merger Agreement to be performed, complied with or satisfied 
by the Company.

          1.3  DELIVERY OF PROXY.  The Stockholder agrees that the Buyer may 
deliver a copy of this Agreement to the Secretary of the Company and to any 
inspector or judges of elections, transfer agents, registrars or others to 
whom such notice may be necessary in order to accomplish the purpose 
described in Section 1.1(a).

                                     -2-



                                   ARTICLE II
                                          
                         REPRESENTATIONS AND WARRANTIES
                               OF THE STOCKHOLDER

          The Stockholder hereby represents and warrants to Buyer and 
Mergerco as follows:

          2.1  AUTHORITY RELATIVE TO THIS AGREEMENT.  The Stockholder has 
full right, power and authority to execute and deliver this Agreement and to 
carry out his obligations hereunder including the right to grant an 
irrevocable proxy with respect to the Proxy Shares and to enter into and 
perform the Escrow Agreement and the Stockholder's agreement to be bound by 
Article 11 of the Merger Agreement (the "Article 11 Agreement"). This 
Agreement, the Escrow Agreement and the Article 11 Agreement have been duly 
and validly executed and delivered by the Stockholder and constitute legal, 
valid and binding agreements of the Stockholder, enforceable against the 
Stockholder in accordance with their respective terms, except as the 
enforceability thereof may be limited by (i) any applicable bankruptcy, 
insolvency, fraudulent conveyance, reorganization, moratorium or other 
similar laws now or hereafter in effect affecting creditors' rights 
generally, and (ii) general principles of equity (regardless of whether 
enforcement is considered in a proceeding in equity or at law).

          2.2  CONSENTS AND APPROVALS; NO VIOLATION.  None of the execution 
and delivery and performance by the Stockholder of this Agreement, the Escrow 
Agreement or the Article 11 Agreement nor the consummation by the Stockholder 
of the transactions contemplated hereby or thereby or compliance by the 
Stockholder with any of the provisions hereof (including the grant of the 
irrevocable proxy with respect to the Proxy Shares) or thereof will (i) 
require any consent, approval, authorization or permit of, or filing with or 
notification to, any governmental or regulatory authority or any court or any 
other third party, except for those described in the Merger Agreement or the 
Schedules thereto; (ii) violate or conflict with any judgment, order, writ, 
injunction, decree, prohibition, statute, rule or regulation applicable to 
the Stockholder; or (iii) result in a default or the breach of any note, 
agreement or other instrument or obligation to which the Stockholder may be 
bound.

          2.3  OWNERSHIP.  As of the date hereof and as of the Effective 
Time, the Stockholder beneficially owns with power to vote 476,756 shares of 
ETS Class B Common Stock, free and clear of any and all claims, liens, 
charges, encumbrances, covenants, conditions, restrictions, voting trust 
arrangements, options and adverse claims or rights whatsoever, except, for 
those granted hereby. The Stockholder does not own of record or beneficially 
any other shares of capital stock of the Company or other securities 
representing or convertible into shares of capital stock of the Company 
except as set forth in the previous sentence. There are no options, warrants, 
calls, commitments or agreements of any nature whatsoever pursuant to which 
any Person will have the right to purchase or otherwise acquire the Proxy 
Shares; except as provided in this Agreement, the Stockholder has not granted 
or agreed to grant any proxy or entered into any voting trust, vote pooling 
or other agreement with respect to the right to vote or give consents or 
approvals of any kind as to the Proxy Shares.

                                     -3-



          2.4  FINDER'S FEES.  Except as set forth in the Merger Agreement or 
the Schedules thereto, there is no investment banker, broker, finder or other 
similar intermediary which has been retained by or is authorized to act on 
behalf, of the Stockholder or any of his Affiliates who might be entitled to 
any fee or commission from Buyer, the Company or any of their Affiliates upon 
consummation of the transactions contemplated by this Agreement or the Merger 
Agreement.

          2.5  ACCESS TO INFORMATION. The Stockholder has received all 
information that he believes is necessary for him to evaluate the 
transactions contemplated by this Agreement, the Escrow Agreement and the 
Merger Agreement and to grant the proxy contemplated by Article I hereof.

          2.6  COOPERATION.  The Stockholder will take all action reasonably 
necessary in order that his representations and warranties set forth in this 
Agreement shall be true and correct at all times during the term of this 
Agreement.
                                          
                                          
                                    ARTICLE III
                                          
                                    TERMINATION

          3.1  TERMINATION.  This Agreement may be terminated at any time by 
mutual consent of all of the parties hereto, and this Agreement will 
terminate automatically if the Merger Agreement is terminated in accordance 
with the terms thereof.

                                     ARTICLE IV
                                          
                             SURVIVAL; INDEMNIFICATION

          4.1  SURVIVAL.  All representations, warranties, covenants and 
agreements contained in this Agreement shall survive (and not be affected in 
any respect by) the Effective Time.

          4.2  STOCKHOLDER'S INDEMNIFICATION.  The Stockholder agrees to 
indemnify, defend, and hold harmless Buyer and Mergerco and their Affiliates 
and their respective officers, directors, employees and agents against and in 
respect of any and all losses, damages, claims, liabilities, actions, suits, 
proceedings, and costs and expenses of defense thereof, including reasonable 
attorney's fees and expenses which fees and expenses will be payable at least 
quarterly suffered or incurred by Buyer, Mergerco or any such other 
indemnified person by reason of, resulting from or arising out of (i) the 
breach or inaccuracy of any representation or warranty of Stockholder 
contained in this Agreement, and (ii) the breach by Stockholder of any 
covenant or other agreement which is contained in this Agreement.

                                     -4-



                                     ARTICLE V
                                          
                                   MISCELLANEOUS

          5.1  NOTICES.  All notices or other communications required or 
permitted hereunder shall be given in writing and shall be delivered or sent, 
by telecopy (or like transmission) with a conforming copy by first class U.S. 
Mail, postage prepaid, by delivery against receipt from the parties to whom 
it is given, by registered or certified U. S. Mail, or by overnight express 
delivery service as follows:



                                               
               If to the Representative:          Harry Stephenson
                                                  Environmental Test Systems, Inc.
                                                  23575 County Road 106
                                                  P. O. Box 4659
                                                  Elkhart, IN 46514-0659
                                                  Fax No.: (219) 262-2495

               with a copy (which                 William R. Neale, Esq.
               shall not constitute               Krieg, DeVault, Alexander & Capehart
               notice) to:                        One Indiana Square, Suite 2800
                                                  Indianapolis, IN  46204-2017
                                                  Fax No. (317) 636-1507

               If to Hach:                        Gary R. Dreher
                                                  Hach Company
                                                  5600 Lindbergh Drive
                                                  Loveland, CO  80538
                                                  Fax No. (970) 962-6740

               with a copy (which                 Robert O. Case, Esq.
               shall not constitute               McBride, Baker & Coles
               notice) to:                        500 W. Madison St., 40th Floor
                                                  Chicago, IL  60661-2511
                                                  Fax No. (312) 993-9350


or such other address as a party may from time to time designate in writing 
in accordance with this Section.  All such notices, requests or other 
communication shall be effective (a) if delivered by hand, when delivered; 
(b) if mailed in the manner provided herein, five (5) business days after 
deposit with the United States Postal Service except that confirmation copies 
of telecopy notice shall be deemed to be effective on the date mailed; (c) if 
delivered by overnight express delivery service, on the next business day 
after deposit with such service; and (d) if by telecopier, on the next 
business day if also confirmed by mail in the manner provided herein.

                                     -5-



          5.2  HEADINGS.  The article and section headings herein are for 
convenience of reference only, do not constitute part of this Agreement and 
shall not be deemed to limit or otherwise affect any provision hereof.

          5.3  ASSIGNMENT.  This Agreement and all of the provisions hereof 
shall be binding upon and inure to the benefit of the parties hereto and 
their respective successors and permitted assigns (which shall include any 
successor by merger or consolidation, or by transfer or purchase of all or 
substantially all the assets or business, of any party hereto); PROVIDED that 
neither this Agreement nor any of the rights, interests, or obligations 
hereunder may be assigned by either party without the prior written consent 
of the other.

          5.4  ENTIRE AGREEMENT.  This Agreement, the Merger Agreement, the 
Escrow Agreement and the Confidentiality Agreements and other agreements 
referred to in the Merger Agreement embody the entire agreement and 
understanding of the parties with respect to the transactions contemplated 
hereby and thereby and supersede all prior written or oral commitments, 
arrangements or understandings with respect thereto.

          5.5  MODIFICATIONS, AMENDMENTS AND WAIVERS.  (a) At any time, to 
the extent permitted by law, (i) the parties hereto may, only by written 
agreement, modify, amend or supplement any term or provision of this 
Agreement and (ii) any term or provision of this Agreement may be waived only 
in writing by the party which is entitled to the benefits thereof.

               (b)  No failure or delay by any party in exercising any right, 
power or privilege hereunder shall operate as a waiver thereof nor shall any 
single or partial exercise thereof preclude any other or further exercise 
thereof or the exercise of any other right, power or privilege. The rights 
and remedies herein provided shall be cumulative and not exclusive of any 
rights or remedies provided by law.

          5.6  COUNTERPARTS.  This Agreement may be executed in any number of 
counterparts, all of which shall be considered one and same agreement and 
each of which shall be deemed an original. This Agreement shall become 
effective when each party hereto shall have received counterparts hereof 
signed by all of the other parties hereto.

          5.7  NO THIRD PARTY BENEFICIARY.  Nothing in this Agreement is 
intended, or shall be construed, to confer upon or give any person other than 
the parties hereto, the indemnified persons referred to in Section 4.2 and 
their respective successors and permitted assigns, any rights or remedies 
under or by reason of this Agreement.

          5.8  SEVERABILITY.  Any term or provision of this Agreement which 
is invalid or unenforceable in any jurisdiction shall, as to such 
jurisdiction, be ineffective to the extent of such invalidity or 
unenforceability without rendering invalid or unenforceable the remaining 
terms and provisions of this Agreement, or affecting the validity or 
enforceability of any of the terms or provisions of this Agreement in any 
other jurisdiction.

                                     -6-



          5.9  SPECIFIC PERFORMANCE.  Each of the parties hereto acknowledges 
and agrees that irreparable injury would occur in the event any of the 
provisions of this Agreement were not performed in accordance with its 
specific terms or were otherwise breached. It is accordingly agreed that the 
parties shall, in addition to any other remedy to which they may be entitled 
at law or in equity, be entitled to seek an injunction or injunctions to 
prevent breaches of the provisions of this Agreement and to seek to enforce 
specifically this Agreement and the terms and provisions hereof in any action 
instituted in any court.

          5.10 EXPENSES.  Except as set forth herein, all costs and expenses 
incurred in connection with this Agreement shall be paid by the party 
incurring such cost or expense.

          5.11 GOVERNING LAW.  THIS AGREEMENT SHALL BE GOVERNED BY AND 
CONSTRUED IN ACCORDANCE WITH THE INTERNAL LAWS OF THE STATE OF DELAWARE.

                                     -7-



                   [ SIGNATURE PAGE FOR STOCKHOLDER'S AGREEMENT]


IN WITNESS WHEREOF, the parties hereto have caused the Agreement to be duly 
executed as of the day and year written above.

                                                 HACH COMPANY




                                                 By: /s/ Bruce J. Hach 
                                                    ---------------------------
                                                     Bruce J. Hach, President




                                                 /s/ Harry Stephenson
                                                 ------------------------------
                                                 Harry Stephenson

                                     -8-