AMENDMENT  NO. 1 TO HACH  COMPANY 1993 STOCK OPTION PLAN AS AMENDED AND RESTATED
AS OF NOVEMBER 25, 1997

This  Amendment No. 1 to the Hach Company 1993 Stock Option Plan, as Amended and
Restated  as of November  25,  1997 (the  "Plan"),  is made by Hach  Company,  a
Delaware corporation (the "Company") with reference to the following facts:

     A.   By action of the Board of  Directors  of the Company on  February  24,
          1998,  the 1993 Stock  Option  Plan was  amended  and  restated  as of
          November 25, 1997.

     B.   Subsequent  to  that  amendment  and  restatement,   the  Company  has
          determined  to increase the number of shares of Class A Common  Stock,
          $1.00 par value, which may be optioned and sold under the Plan, and to
          amend Section 3 of the Plan to effect that increase.

     C.   It is also appropriate to amend Section 8(c) of the Plan to make clear
          that  only  shares  of  Common  Stock  may be used  to pay for  shares
          purchased upon exercise of options granted before the establishment of
          Class A Common Stock.

Now therefore,  the Company,  pursuant to action by its board of directors taken
on April 27, 1998,  hereby  amends the Plan as follows,  such  amendments  to be
effective as of November 25, 1997:

     1.   The first  paragraph  of  Section 3 of the Plan is  amended to read in
          full as follows:

          Subject  to the  provisions  of Section  11 of the Plan,  the  maximum
          aggregate  number of Shares  which may be optioned  and sold under the
          Plan is Six Hundred  Twenty-Five  Thousand  (625,000) shares of Common
          Stock and Two Million,  One Hundred Twenty-Five  Thousand  (2,125,000)
          shares of Class A Common  Stock.  The  Shares may be  authorized,  but
          unissued, or reacquired shares of Stock.

     2.   Section 8(c) of the Plan is amended to read in full as follows:

          (c) The  consideration  to be paid for the  Shares to be  issued  upon
          exercise  of an  Option,  including  the method of  payment,  shall be
          determined  by the Board at the time of grant and may  consist of cash
          and/or  check.  Payment  may  also be made by  delivering  a  properly
          executed  exercise notice together with irrevocable  instructions to a
          broker to promptly  deliver to the Company the amount of sale proceeds
          necessary to pay the exercise  price. An Optionee may also in addition
          pay all or part of the  purchase  price  with  Shares of Common  Stock
          and/or Shares of Class A Common Stock,  provided,  however that in the
          case of  Options  granted  before  September  10,  1997,  the date the
          Company's dual class capital structure became effective,  options must
          be exercised  in tandem (i.e.  both the option of Common Stock and the
          companion  option  on Class A Common  Stock  which  resulted  from the
          change to a dual class capital structure must be exercised at the same
          time) and, provided  further,  that the number of shares of each class
          which may be so utilized in payment of the options shall be subject to
          such additional  rules and  restrictions as the Committee or Board may
          promulgate for such  exercises.  Shares used to pay the exercise price
          shall be valued at their fair market value on the exercise date.  With
          the  approval of the Board,  the  Optionee may borrow from the Company
          all or any portion of the funds  needed to pay the price on such terms
          and conditions as the Board deems  appropriate,  provided that (i) the
          interest  rate for any such loan by the Company shall not be less than
          the   "applicable   federal   rate"  (as   defined  by  Code   Section
          127(d)(1)(A))  in effect on the date of such loan or any other rate as
          necessary to avoid the  imputation of interest under the Code or other
          applicable  law,  (ii) proceeds of the loan are used solely to pay the
          exercise price of an Option  granted  pursuant to this Plan, and (iii)
          the Optionee  executes a promissory  note and such other  documents as
          the Board deems appropriate to evidence the Optionee's indebtedness to
          the  Company,  and  pledges the Shares  received in exchange  for such
          borrowed funds as collateral for such loan.

     3.   The  foregoing  amendment  to Section 3 shall  require  approval of or
          ratification by the stockholders of the Company.

Adopted  pursuant  to  Board  Resolution  of  April  27,  1998  and  subject  to
Stockholder approval.