STRATEGIC DIAGNOSTICS INC/DE/
SC 13D, 1997-01-09
MISCELLANEOUS CHEMICAL PRODUCTS
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<PAGE>



                                    UNITED STATES
                          SECURITIES AND EXCHANGE COMMISSION
                                Washington, D.C. 20549


                                     SCHEDULE 13D


                      Under the Securities Exchange Act of 1934


                              Strategic Diagnostics Inc.
- -------------------------------------------------------------------------------
                                   (Name of Issuer)

                        Common Stock, par value $.01 per share
- -------------------------------------------------------------------------------
                            (Title of Class of Securities)


                                      862700101
- -------------------------------------------------------------------------------
                                    (CUSIP Number)


               Morton Collins,  DSV Partners IV, 221 Nassau Street, 
                         Princeton, NJ  08542  (609)924-6420

- -------------------------------------------------------------------------------
             (Name, Address and Telephone Number of Person Authorized to 
                         Receive Notices and Communications)


                                  December 30, 1996

- -------------------------------------------------------------------------------
               (Date of Event which Requires Filing of this Statement)


If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box .
                                                                            
NOTE:  Six copies of this statement, including all exhibits, should be filed
with the Commission.  SEE Rule 13d-1(a) for other parties to whom copies are to
be sent.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).


                                 Page   1
                                       ---


<PAGE>

                                     SCHEDULE 13D



CUSIP NO. 862700101                          PAGE   2


- ----------------------------------------------------------------------------
 1   NAME OF REPORTING PERSON                                             
     S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON                    
                                                                          
     DSV Partners IV                                                      
                                                                     
- ----------------------------------------------------------------------------
 2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*          (a)  / /     
                                                                          
                                                                (b)  / /    
- ----------------------------------------------------------------------------
 3   SEC USE ONLY                                                         
                                                                          
- ----------------------------------------------------------------------------
 4   SOURCE OF FUNDS*  OO                                                 
                                                                          
- ----------------------------------------------------------------------------
 5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS                   / /  
     REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)                              
                                                                          
- ----------------------------------------------------------------------------
 6   CITIZENSHIP OR PLACE OF ORGANIZATION                                 
                                                                          
     New Jersey                                                           
- ----------------------------------------------------------------------------
               7  SOLE VOTING POWER                                  
  NUMBER OF       1,297,177                                          
   SHARES     --------------------------------------------------------------
 BENEFICIALLY  8  SHARED VOTING POWER                               
   OWNED BY                                                          
    EACH          N/A                                               
  REPORTING   --------------------------------------------------------------
   PERSON      9  SOLE DISPOSITIVE POWER                            
    WITH                                                             
                  1,297,177                                         
              --------------------------------------------------------------
              10  SHARED DISPOSITIVE POWER                          
                                                                     
                   N/A                                              
- ----------------------------------------------------------------------------
11    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON    
                                                                      
      1,297,177                                                       
- ----------------------------------------------------------------------------
12    CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11)                     / /
      EXCLUDES CERTAIN SHARES*                                        
                                                                      
- ----------------------------------------------------------------------------

13    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)             
      9.1%                                                           
- ----------------------------------------------------------------------------
14    TYPE OF REPORTING PERSON*                                       
      PN                                                              
- ----------------------------------------------------------------------------

                         SEE INSTRUCTIONS BEFORE FILLING OUT!


<PAGE>
 

                                SCHEDULE 13D STATEMENT

ITEM 1.       SECURITY AND ISSUER.

              This statement relates to the shares of Common Stock, par value
              $.01 per share (the "Common Stock") of Strategic Diagnostics
              Inc., a Delaware corporation (the "Issuer").  The principal
              executive offices of the Issuer are located at 128 Sandy Drive,
              Newark, Delaware 19713.     

ITEM 2.       IDENTITY AND BACKGROUND.

              DSV Partners IV is a New Jersey limited partnership.  Its office
              is located at 221 Nassau Street, Princeton, New Jersey 08542. 
              DSV Partners IV invests in technology based companies.  The 
              sole general partner of DSV Partners IV is DSV Management Ltd. 
              which is a New Jersey limited partnership located at 221 Nassau 
              Street, Princeton, New Jersey 08542. Set forth
              below is the name and address of each General Partner of DSV
              Management Ltd.:

                        James R. Bergman
                        DSV Partners IV
                        1920 Main Street
                        Suite 820
                        Irvine, CA 92614

                        Morton Collins
                        DSV Partners IV
                        221 Nassau Street
                        Princeton, NJ 08542

                        John Park
                        DSV Partners IV
                        221 Nassau Street
                        Princeton, NJ 08542

                        John K. Clarke
                        DSV Partners IV
                        221 Nassau Street
                        Princeton, NJ 08542



                                 Page   3
                                       ---

<PAGE>

              None of DSV Partners IV, DSV Management Ltd. or any General 
              Partner of DSV Management Ltd. has been convicted in a criminal 
              proceeding (excluding traffic violations and similar misdemeanors)
              during the past five years, or have been a party to a civil 
              proceeding of a judicial or administrative body of competent 
              jurisdiction and as a result of such proceeding was or is subject 
              to a judgment, decree or final order enjoining future violations 
              of or prohibiting activities subject to, federal or state 
              securities laws or finding any violation of such laws.

ITEM 3.       SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.

              DSV Partners IV was the beneficial owner of 1,463,980 shares of 
              Series A Convertible Preferred Stock of Strategic  Diagnostics 
              Inc. ("SDI") and 275,000 immediately exercisable warrants to 
              purchase shares of Common Stock of SDI.  On December 30, 1996, SDI
              merged with and into EnSys Environmental Products, Inc. ("EnSys").
              The surviving corporation, EnSys, was subsequently renamed 
              Strategic Diagnostics Inc.  Each share of SDI common and preferred
              stock was converted into .7392048 shares of the Issuer.  Each 
              warrant to purchase SDI common stock was converted into .7818026 
              warrants to purchase shares of the Issuer's common stock.  Each 
              share of Series A Convertible Preferred Stock of the Issuer is 
              currently convertible into one share of Common Stock of the 
              Issuer.  Accordingly, through its ownership of Series A 
              Convertible Preferred Stock, DSV Partners IV beneficially owns 
              1,082,181 shares of Common Stock.  Moreover, through its ownership
              of warrants to purchase Common Stock, DSV Partners IV beneficially
              owns an additional 214,996 shares of Common Stock, for an 
              aggregate of 1,297,177 shares beneficially owned.
              
                                               Page   4
                                                     ---

<PAGE>

ITEM 4.       PURPOSE OF TRANSACTION.

              DSV Partners IV acquired the shares of the Issuer for investment
              purposes.  DSV Partners IV will monitor market conditions and
              pursue sales from time to time although there can be no assurance
              of the total number of shares to be sold.  DSV Partners IV may
              from time to time acquire additional securities (through one or
              more market purchases or purchases in private transactions) or
              dispose of all or a portion of the securities which it now owns
              or hereafter may acquire (through one or more market or private
              transactions or distributions to partners in accordance with the
              partnership agreement).  Except as set forth above, DSV Partners
              IV does not have any present plans or proposals which relate to
              or would result in any of the actions described in paragraphs (a)
              through (j) of Item 4 of Schedule 13D. 
              
ITEM 5.       INTEREST IN SECURITIES OF THE ISSUER.

              DSV Partners IV beneficially owns: (i) 1,082,181 shares of Common
              Stock through its ownership of Series A Convertible Preferred
              Stock and (ii) 214,996 shares of Common Stock through its 
              ownership of warrants to purchase Common Stock, for an aggregate
              of 1,297,177 shares of Common Stock beneficially owned, which
              equals 9.1% of the outstanding shares of Common Stock of the
              Issuer.
              

ITEM 5(B).    Number of shares as to which DSV Partners IV has:
    
              sole power to vote or to direct the vote: 1,297,177

              shared power to vote or to direct the vote: None

              sole power to dispose or to direct the disposition: 
              1,297,177

              shared power to dispose or to direct the disposition: None



                                 Page   5
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<PAGE>

ITEM 5(C).    None of DSV Partners IV, DSV Management Ltd. or any General 
              Partner of DSV Management Ltd. has been a party to any 
              transaction in the Common Stock during the sixty day period 
              ending on the date of this Statement on Schedule 13D, other than 
              the transactions described herein. 

ITEM 5(D).    Not applicable.  
                   
    
ITEM 6.       CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH    
              RESPECT TO SECURITIES OF THE ISSUER. 

              DSV Partners IV has signed a "lock-up" agreement with the Issuer,
              pursuant to which DSV has agreed not to sell or transfer its
              shares of the Issuer's Common or Preferred Stock for a period of
              six months from the date of the merger between SDI and the
              Issuer.  DSV Partners IV has also entered into a Registration
              Rights Agreement with the Issuer, dated December 30, 1996, which
              provides for (i) certain demand registration rights and (ii) the
              right to require the Issuer to include Common Stock owned by DSV
              Partners IV in any other registration of Issuer's Common Stock.

              The  terms of the Series A Convertible Preferred Stock are set
              forth in the Fourth Amended and Restated Certificate of
              Incorporation of the Issuer.  

ITEM 7.       MATERIAL TO BE FILED AS EXHIBITS.

              Exhibit 1 -    Letter Agreement dated December 30, 1996 between
                             Issuer and DSV.

              Exhibit 2 -    Registration Rights Agreement dated December 30,
                             1996 between Issuer and certain holders of
                             Issuer's Common Stock.

              Exhibit 3 -    Warrants W-12/30/96 - A through G, issued by EnSys
                             in favor of DSV.

              Exhibit 4 -    Fourth Amended and Restated Certificate of
                             Incorporation of the Issuer.




                                 Page   6
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<PAGE>

                                      SIGNATURE

    After reasonable 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.


                                  DSV PARTNERS IV


Dated: January 8, 1997            By: DSV MANAGEMENT LTD.
                                      its General Partner

                                  By: Morton Collins
                                      a General Partner

                                      /s/ Morton Collins
                                         --------------
                                  Page 7
                                      ---



<PAGE>

                                                        EXHIBIT 1


                                       December 30, 1996


EnSys Environmental Products, Inc.
4222 Emperor Boulevard
Durham, North Carolina 27703

Dear Ladies and Gentlemen:

     In consideration of the benefit to the stockholders of Strategic 
Diagnostics Inc. ("Company") of the merger of the Company with and into 
EnSys Environmental Products, Inc. ("EnSys"), pursuant to the Agreement and 
Plan of Merger between the Company and EnSys dated as of October 11, 1996, 
and for other good and valuable consideration, the receipt of which is hereby 
acknowledged, the undersigned hereby agrees that, without the prior written 
consent of EnSys, he or she will not sell, contract to sell, or otherwise 
dispose of for value, any of the EnSys Preferred Stock, Common Stock or any 
security exchangeable or exercisable for or convertible into EnSys Common 
Stock, beneficially owned by the undersigned until the date which is six (6) 
months from the date hereof; provided that the undersigned may pledge or 
cause to be pledged any or all of such shares or other securities in bona 
fide loan transactions with established financial lending institutions.


                                       DSV PARTNERS IV

                                       By:  DSV MANAGEMENT LTD.,
                                            its General Partner

                                            By:  Morton Collins,
                                                 a General Partner

                                                 /s/ Morton Collins
                                                 -----------------------------




<PAGE>

                                                   EXHIBIT 2




                                   December 30, 1996 





To each of the Original Holders
listed on the signature
pages hereto

Dear Sirs:

         This agreement is made in connection with the Agreement and Plan of
Merger, dated as of October 11, 1996 (the "Merger Agreement") by and between
Strategic Diagnostics Inc., a Delaware corporation ("SDI") and EnSys
Environmental Products, Inc., a Delaware corporation (the "Company"), pursuant
to which SDI shall be merged with and into the Company in accordance with the
applicable provisions of the Delaware General Corporation Law and the terms of
the Merger Agreement.  The merger consideration received by the Original Holders
(as hereinafter defined) includes, common stock, par value $.01, of the Company
(the "Common Stock"), Series A Convertible Preferred Stock (the "Preferred
Stock"), par value $.01, of the Company that is convertible into shares of
Common Stock, and warrants (the "Warrants") to purchase shares of Common Stock. 
The Company covenants and agrees with each of you (the "Original Holders") as
follows:

         1.   Certain Definitions.  As used in this Agreement, the following
terms shall have the following respective meanings:

              "Commission" shall mean the Securities and Exchange Commission,
or any other federal agency at the time administering the Securities Act.

              "Common Stock" shall mean the Common Stock, $0.01 par value, of
the Company, as constituted as of the date of this Agreement.

              "Conversion Shares" shall mean shares of Common Stock issued upon
conversion of the Preferred Shares, together with any shares of Common Stock
issued on or with respect to other Conversion Shares by way of a stock split,
stock dividend or the like.

              "Exchange Act" shall mean the Securities Exchange Act of 1934, as
amended, or any similar federal statute, and the rules and regulations of the
Commission thereunder, all as the same shall be in effect at the time.

<PAGE>

              "Perkin-Elmer Shares" shall mean 1,308,724 shares of Common Stock
issued pursuant to the Merger Agreement to The Perkin-Elmer Corporation.

              "Preferred Shares" shall mean an aggregate of 2,164,362 shares of
Preferred Stock issued pursuant to the Merger Agreement to DSV Partners IV,
Edison Venture Fund II, L.P. and Edison Venture Fund II-Pa, L.P. 

              "Registration Expenses" shall mean the expenses so described in
Section 8.

              "Restricted Stock" shall mean the Conversion Shares, Perkin-Elmer
Shares, and Warrant Shares, excluding Conversion Shares, Perkin-Elmer Shares,
and Warrant Shares which (a) have been registered under the Securities Act
pursuant to an effective registration statement filed thereunder and disposed of
in accordance with the registration statement covering them or (b) are eligible
for public sale without limitation as to amount pursuant to Rule 144 or Rule 145
under the Securities Act.

              "Securities Act" shall mean the Securities Act of 1933, as
amended, or any similar federal statute, and the rules and regulations of the
Commission thereunder, all as the same shall be in effect at the time.

              "Selling Expenses" shall mean the expenses so described in
Section 8.

              "Transfer" shall include any disposition of any Preferred Shares,
Perkin-Elmer Shares, Conversion Shares and Warrant Shares or of any interest
therein which would constitute a sale thereof within the meaning of the
Securities Act.

              "Warrant Shares" shall mean shares of Common Stock issued upon
exercise of the Warrants, together with any shares of Common Stock issued on or
with respect to other Warrant Shares by way of stock split, stock dividend or
the like.

         2.   Restrictive Legend.  The Preferred Shares, Perkin-Elmer Shares,
Conversion Shares and Warrant Shares shall not be transferable, except upon the
conditions specified in Sections 2 and 3 hereof, which conditions are intended
to ensure compliance with the provisions of the Securities Act in respect of the
Transfer thereof.  Each certificate representing Preferred Shares, Perkin-Elmer
Shares, Conversion Shares or Warrant Shares shall, except as otherwise provided
in this Section 2 or in Section 3, be stamped or otherwise imprinted with a
legend substantially in the following form:

                                       2

<PAGE>

    "THIS SECURITY HAS NOT BEEN REGISTERED FOR SALE UNDER THE SECURITIES
    ACT OF 1933 AND MAY NOT BE TRANSFERRED OR OTHERWISE DISPOSED OF EXCEPT
    IN COMPLIANCE WITH THAT CERTAIN REGISTRATION RIGHTS AGREEMENT, DATED
    DECEMBER 30, 1996 AMONG THE COMPANY AND THE SIGNATORIES THERETO AND
    THE SECURITIES ACT OF 1933, AS AMENDED."

         3.   Notice of Proposed Transfer.  Prior to any proposed Transfer of
any Preferred Shares, Perkin-Elmer Shares, Conversion Shares or Warrant Shares
(other than under the circumstances described in Sections 4 or 5), the holder
thereof shall give written notice to the Company of its intention to effect such
Transfer.  Each such notice shall describe the manner of the proposed Transfer
and, if requested by the Company, shall be accompanied by an opinion of counsel
satisfactory to the Company to the effect that the proposed Transfer may be
effected without registration under the Securities Act, whereupon the holder of
such stock shall be entitled to Transfer such stock in accordance with the terms
of its notice; provided, however, that no such opinion of counsel shall be
required for a Transfer to one or more partners of an Original Holder (in the
case of an Original Holder that is a partnership) or to an affiliated
corporation of an Original Holder (in the case of an Original Holder that is a
corporation), if, with respect to such Transfer, the transferee agrees in
writing to be subject to the terms of Sections 2, 3 and 10 hereof, to the same
extent as if such transferee were originally a signatory to this Agreement. 
Each certificate for Preferred Shares, Perkin-Elmer Shares, Conversion Shares or
Warrant Shares transferred as above provided shall bear the legend set forth in
Section 2, except that such certificate shall not bear such legend if (i) such
Transfer is in accordance with the provisions of Rule 144 (or any other rule
permitting public sale without registration under the Securities Act) or (ii)
the opinion of counsel referred to above is to the further effect that the
transferee and any subsequent transferee (other than an affiliate of the
Company) would be entitled to Transfer such securities in a public sale without
registration under the Securities Act.  The restrictions provided for in this
Section 3 shall not apply to securities which are not required to bear the
legend prescribed by Section 2 in accordance with the provisions of that
Section.

         4.   Required Registration.  (a) At any time after the date which is
six (6) months from the date of this Agreement, any two (2) of the three (3)
holders of Restricted Stock acting together as a group may request on two (2)
separate occasions the Company to register under the Securities Act all or any
portion of the shares of Restricted Stock held by such requesting holders for
sale in the manner specified in such notice, provided that the shares of
Restricted Stock for which registration has been

                                       3

<PAGE>


requested shall constitute at least the lesser of (i) 50% of the total shares 
of Restricted Stock originally issued to such holders, or (ii) the remaining 
shares of Restricted Stock held by such holders, but in any event not less 
than 1,500,000 shares of Restricted Stock.  For purposes of this Section 4 
and Sections 5, 12(a) and 12(d), the term "Restricted Stock" shall be deemed 
to include the number of shares of Restricted Stock which would be issuable 
to a holder of Preferred Shares upon conversion of all shares of Preferred 
Stock held by such holder at such time and the number of shares of Restricted 
Stock which would be issuable to a holder of Warrants upon exercise of all 
Warrants held by such holder at such time, provided, however, that the only 
securities which the Company shall be required to register pursuant hereto 
shall be shares of Common Stock, and provided, further, however, that, in any 
underwritten public offering contemplated by this Section 4 or Section 5, the 
holders of Preferred Shares and Warrants shall be entitled to sell such 
Preferred Shares and Warrants to the underwriters for conversion or exercise, 
respectively, and sale of the shares of Common Stock issued upon conversion 
thereof.  Notwithstanding anything to the contrary contained herein, no 
request may be made under this Section 4 within 180 days after the effective 
date of a registration statement filed by the Company covering a firm 
commitment underwritten public offering in which the holders of Restricted 
Stock shall have been entitled to join pursuant to Section 5 and in which 
there shall have been effectively registered at least fifty percent (50%) of 
the shares of Restricted Stock as to which registration shall have been 
requested.

              (b)  Following receipt of any notice under this Section 4, the
Company shall immediately notify all holders of Restricted Stock from whom
notice has not been received and shall use all reasonable efforts to register
under the Securities Act, for public sale in accordance with the method of
disposition specified in such notice from requesting holders, the number of
shares of Restricted Stock specified in such notice (and in all notices received
by the Company from other holders within 30 days after the giving of such notice
by the Company).  If such method of disposition shall be an underwritten public
offering, the Company may designate the managing underwriter of such offering,
subject to the approval of the holders of a majority of the shares of Restricted
Stock to be sold in such offering, which approval shall not be unreasonably
withheld, conditioned or delayed.  The Company shall be obligated to register
Restricted Stock pursuant to this Section 4 on two occasions only, provided,
however, that such obligation shall be deemed satisfied only when a registration
statement covering at least the lesser of (i) 50% of the total shares of
Restricted Stock originally issued or (ii) 75% of the shares of Restricted Stock
specified in notices

                                       4

<PAGE>


received as aforesaid, for sale in accordance with the method of disposition 
specified by the requesting holders, shall have become effective; provided, 
further, however, that any registration proceeding begun pursuant to this 
Section 4 which is subsequently withdrawn at the request of the holders of a 
majority of the shares of Restricted Stock requested to be registered shall 
count toward such two registration statements which the holders of the shares 
of Restricted Stock have the right to cause the Company to effect pursuant to 
this Section 4.

              (c)  The Company shall be entitled to include in any registration
statement referred to in this Section 4, for sale in accordance with the method
of disposition specified by the requesting holders, shares of Common Stock to be
sold by the Company for its own account, or any issued and outstanding shares of
Common Stock to be sold by others except as and to the extent that, in the
opinion of the managing underwriter (if such method of disposition shall be an
underwritten public offering), such inclusion would adversely affect the
marketing of the Restricted Stock to be sold.

         5.   Incidental Registration.  If the Company at any time (other than
pursuant to Section 4) proposes to register any of its securities under the
Securities Act for sale to the public, whether for its own account or for the
account of other security holders or both (except with respect to registration
statements on Forms S-4 or another form not available for registering the
Restricted Stock for sale to the public), each such time it will give written
notice to all holders of outstanding Restricted Stock of its intention so to do.
Upon the written request of any such holder received by the Company within 30
days after the giving of any such notice by the Company, to register any of its
Restricted Stock (which request shall state the intended method of disposition
thereof), the Company will use all commercially reasonable efforts (subject to
the rights of any holders of securities of the Company, other than the Company,
included in such registration) to cause the Restricted Stock as to which
registration shall have been so requested to be included in the securities to be
covered by the registration statement proposed to be filed by the Company, all
to the extent requisite to permit the sale or other disposition by the holder
(in accordance with its written request) of such Restricted Stock so registered.
In the event that any registration pursuant to this Section 5 shall be, in whole
or in part, an underwritten public offering of Common Stock, the number of
shares of Restricted Stock as a group to be included in such an underwriting may
be reduced (pro rata among the holders of Restricted Stock based upon the number
of shares of Restricted Stock owned by such holders) if and to the extent that
the managing underwriter shall be of the opinion that such inclusion would
adversely affect the

                                       5

<PAGE>


marketing of the securities to be sold by the Company or other holder of 
securities of the Company.  Notwithstanding the foregoing provisions, the 
Company may withdraw any registration statement referred to in this Section 5 
without thereby incurring any liability to the holders of Restricted Stock.

         6.   Holdback Agreement.  If the Company at any time shall register
shares of Common Stock under the Securities Act (including any registration
pursuant to Sections 4 and 5) for sale to the public, the Original Holders shall
not sell publicly, make any short sale of, grant an option for the purchase of,
or otherwise dispose of, any shares of Restricted Stock (other than those shares
of Common Stock included in such registration pursuant to Sections 4 or 5)
without the prior written consent of the Company for a period designated by the
Company in writing to the holders of shares of Restricted Stock, which period
shall not begin more than 10 days prior to the effectiveness of the registration
statement pursuant to which such public offer will be made and shall not last
more than 180 days after the effective date of such registration statement.

         7.   Registration Procedures.  If and whenever the Company is required
by the provisions of Sections 4 or 5 to use all reasonable efforts or all
commercially reasonable efforts to effect the registration of any shares of
Restricted Stock under the Securities Act, the Company will, as expeditiously as
possible:

              (a)  prepare and file with the Commission a registration
statement on Form S-1 or Form S-3 if available with respect to such securities
and use all reasonable efforts to cause such registration statement to become
and remain effective for the period of the distribution contemplated thereby
(determined as hereinafter provided) (subject, in the case of any Incidental
Registration, to the rights of the Company to abandon any such registration as
set forth in Section 5);

              (b)  with respect to any registration pursuant to Section 4,
prepare and file with the Commission such amendments and supplements to such
registration statement and the prospectus used in connection therewith as may be
necessary to keep such registration statement effective for the period specified
above and comply with the provisions of the Securities Act with respect to the
disposition of all Restricted Stock covered by such registration statement in
accordance with the sellers' intended method of disposition set forth in such
registration statement for such period;

              (c)   furnish to each seller of Restricted Stock and to each
underwriter such number of copies of the registration

                                       6

<PAGE>


statement and the prospectus included therein (including each preliminary 
prospectus) as such persons reasonably may request in order to facilitate the 
public sale or other disposition of the Restricted Stock covered by such 
registration statement;

              (d)  use all reasonable efforts to register or qualify the
Restricted Stock covered by such registration statement under the securities or
"blue sky" laws of such jurisdictions as the sellers of Restricted Stock or, in
the case of an underwritten public offering, the managing underwriter reasonably
shall request, provided, however, that the Company shall not for any such
purpose be required to qualify generally to transact business as a foreign
corporation in any jurisdiction where it is not so qualified, to consent to
general service of process in any such jurisdiction or submit to liability for
state or local taxes where it is not otherwise liable for such taxes;

              (e)  use all reasonable efforts to list the Restricted Stock
covered by such registration statement with any securities exchange on which the
Common Stock of the Company is then listed;

              (f)  immediately notify each seller of Restricted Stock and each
underwriter under such registration statement, at any time when a prospectus
relating thereto is required to be delivered under the Securities Act, of the
happening of any event of which the Company has knowledge as a result of which
the prospectus contained in such registration statement, as then in effect,
includes an untrue statement of a material fact or omits to state a material
fact required to be stated therein or necessary to make the statements therein
not misleading in light of the circumstances then existing;

              (g)  if the offering is underwritten and at the request of any
seller of Restricted Stock, use all reasonable efforts to furnish on the date
that Restricted Stock is delivered to the underwriters for sale pursuant to such
registration: (i) an opinion, dated such date, of the counsel representing the
Company for the purposes of such registration, in form and substance as is
customarily given to underwriters in an underwritten public offering, addressed
to the underwriters, if any, and to the seller or sellers making such request;
and (ii) at the request of either the underwriters or sellers of Restricted
Stock, a letter dated such date from the independent public accountants retained
by the Company, addressed to the underwriters and to such seller, stating that
they are independent public accountants within the meaning of the Securities Act
and that, in the opinion of such accountants, the financial statements of the
Company included in the registration statement or the prospectus, or any
amendment or supplement

                                       7

<PAGE>


thereof, comply as to form in all material respects with the applicable 
accounting requirements of the Securities Act, and such letter shall 
additionally cover such other financial matters (including information as to 
the period ending no more than five business days prior to the date of such 
letter) with respect to such registration as such underwriters reasonably may 
request; and

              (h)  make reasonably available for inspection by each seller of
Restricted Stock, any underwriter participating in any distribution pursuant to
such registration statement, and any attorney, accountant or other agent
retained by such seller or underwriter, all financial and other records,
pertinent corporate documents and properties of the Company, and use all
reasonable efforts to cause the Company's officers, directors and employees to
supply all information reasonably requested by any such seller, underwriter,
attorney, accountant or agent in connection with such registration statement, in
each case as and to the extent necessary to permit the sellers to conduct a
reasonable investigation within the meaning of the Securities Act.  To minimize
disruption and expense to the Company during the course of the registration
process, the sellers will act through a single law firm and a single accounting
firm and will enter into confidentiality agreements with the Company in form and
substance reasonably satisfactory to the Company and the sellers prior to
receiving any confidential or proprietary information of the Company.

         For purposes of Section 7(a) and 7(b) and of Section 4(c), the period
of distribution of Restricted Stock in a firm commitment underwritten public
offering shall be deemed to extend until each underwriter has completed the
distribution of all securities purchased by it, and the period of distribution
of Restricted Stock in any other registration shall be deemed to extend until
the earlier of the sale of all Restricted Stock covered thereby, or nine (9)
months after the effective date thereof.

         In connection with each registration hereunder, the sellers of
Restricted Stock will furnish to the Company in writing such information with
respect to themselves and the proposed distribution by them as reasonably shall
be necessary in order to assure compliance with federal and applicable state
securities laws.

         In connection with each registration pursuant to Sections 4 or 5
covering an underwritten public offering, the Company and each seller agree to
enter into a written agreement with the managing underwriter selected in the
manner herein provided in such form and containing such provisions as are

                                       8

<PAGE>

customary in the securities business for such an arrangement between such
underwriter and companies of the Company's size and investment stature.

         8.   Expenses.  All expenses (both third party and internal) incurred
by the Company in complying with Sections 4 and 5, including, without
limitation, all registration and filing fees, printing expenses, fees and
disbursements of counsel and independent public accountants for the Company,
fees and expenses (including counsel fees) incurred in connection with complying
with state securities or "blue sky" laws, fees of the National Association of
Securities Dealers, Inc., transfer taxes, fees of transfer agents and
registrars, costs of insurance, but excluding any Selling Expenses, are called
"Registration Expenses".  All underwriting discounts and selling commissions
applicable to the sale of Restricted Stock, and all fees and disbursements of
legal counsel for the sellers of Restricted Stock, are called "Selling
Expenses".

         The Company will pay all Registration Expenses in connection with each
registration statement under Sections 4 or 5. All Selling Expenses in connection
with each registration statement under Sections 4 or 5 shall be borne by the
participating sellers in proportion to the number of shares sold by each, or by
such participating sellers other than the Company (except to the extent the
Company shall be a seller) as they may agree.

         9.   Indemnification and Contribution.  (a) In the event of a
registration of any of the Restricted Stock under the Securities Act pursuant to
Sections 4 or 5, the Company will indemnify and hold harmless each seller of
such Restricted Stock thereunder, each underwriter of such Restricted Stock
thereunder and each other person, if any, who controls such seller or
underwriter within the meaning of the Securities Act, against any losses,
claims, damages or liabilities, joint or several, to which such seller,
underwriter or controlling person may become subject under the Securities Act or
otherwise, insofar as such losses, claims, damages or liabilities (or actions in
respect thereof) arise out of or are based upon any untrue statement or alleged
untrue statement of any material fact contained in any registration statement
under which such Restricted Stock was registered under the Securities Act
pursuant to Sections 4 or 5, any preliminary prospectus or final prospectus
contained therein, or any amendment or supplement thereof, or arise out of or
are based upon the omission or alleged omission to state therein a material fact
required to be stated therein or necessary to make the statements therein not
misleading, and will reimburse each such seller, each such underwriter and each
such controlling person for any legal or other expenses reasonably incurred by

                                       9

<PAGE>

them in connection with investigating or defending any such loss, claim, damage,
liability or action, provided, however, that the Company will not be liable in
any such case if and to the extent that any such loss, claim, damage or
liability arises out of or is based upon an untrue statement or alleged untrue
statement or omission or alleged omission so made in conformity with information
furnished by any such seller, any such underwriter or any such controlling
person in writing specifically for use in such registration statement or
prospectus.

              (b)  In the event of a registration of any of the Restricted
Stock under the Securities Act pursuant to Sections 4 or 5, each seller of such
Restricted Stock thereunder, severally and not jointly, will indemnify and hold
harmless the Company, each person, if any, who controls the Company within the
meaning of the Securities Act, each officer of the Company who signs the
registration statement, each director of the Company, each underwriter and each
person who controls any underwriter within the meaning of the Securities Act,
against all losses, claims, damages or liabilities, joint or several, to which
the Company or such officer, director, underwriter or controlling person may
become subject under the Securities Act or otherwise, insofar as such losses,
claims, damages or liabilities (or actions in respect thereof) arise out of or
are based upon any untrue statement or alleged untrue statement of any material
fact contained in the registration statement under which such Restricted Stock
was registered under the Securities Act pursuant to Sections 4 or 5, any
preliminary prospectus or final prospectus contained therein, or any amendment
or supplement thereof, or arise out of or are based upon the omission or alleged
omission to state therein a material fact required to be stated therein or
necessary to make the statements therein not misleading, and will reimburse the
Company and each such officer, director, underwriter and controlling person for
any legal or other expenses reasonably incurred by them in connection with
investigating or defending any such loss, claim, damage, liability or action,
provided, however, that such seller will be liable hereunder in any such case if
and only to the extent that any such loss, claim, damage or liability arises out
of or is based upon an untrue statement or alleged untrue statement or omission
or alleged omission made in reliance upon and in conformity with information
pertaining to such seller, as such, furnished in writing to the Company by such
seller specifically for use in such registration statement or prospectus, and
provided, further, however, that the liability of each seller hereunder shall
not in any event exceed the proceeds received by such seller from the sale of
Restricted Stock covered by such registration statement.

                                      10
<PAGE>

              (c)  Promptly after receipt by an indemnified party hereunder of
notice of the commencement of any action, such indemnified party shall, if a
claim in respect thereof is to be made against the indemnifying party hereunder,
notify the indemnifying party in writing thereof, but the omission so to notify
the indemnifying party shall not relieve it from any liability which it may have
to such indemnified party other than under this Section 9 and shall only relieve
it from any liability which it may have to such indemnified party under this
Section 9 if and to the extent the indemnifying party is prejudiced by such
omission.  In case any such action shall be brought against any indemnified
party and it shall notify the indemnifying party of the commencement thereof,
the indemnifying party shall be entitled to participate in and, to the extent it
shall wish, to assume and undertake the defense thereof with counsel
satisfactory to such indemnified party, and, after notice from the indemnifying
party to such indemnified party of its election so to assume and undertake the
defense thereof, the indemnifying party shall not be liable to such indemnified
party under this Section 9 for any legal expenses subsequently incurred by such
indemnified party in connection with the defense thereof other than reasonable
costs of investigation and of liaison with counsel so selected, provided,
however, that, if the defendants in any such action include both the indemnified
party and the indemnifying party and the indemnified party shall have reasonably
concluded that there may be reasonable defenses available to it which are
different from or additional to those available to the indemnifying party or if
the interests of the indemnified party reasonably may be deemed to conflict with
the interests of the indemnifying party, the indemnified party shall have the
right to select a separate counsel and to assume such legal defenses and
otherwise to participate in the defense of such action, with the expenses and
fees of such separate counsel and other expenses related to such participation
to be reimbursed by the indemnifying party as incurred.

              (d)  In order to provide for just and equitable contribution to
joint liability under the Securities Act in any case in which either (i) any
holder of Restricted Stock exercising rights under this Agreement, or any
controlling person of any such holder, makes a claim for indemnification
pursuant to this Section 9 but it is judicially determined (by the entry of a
final judgment or decree by a court of competent jurisdiction and the expiration
of time to appeal or the denial of the last right of appeal) that such
indemnification may not be enforced in such case notwithstanding the fact that
this Section 9 provides for indemnification in such case, or (ii) contribution
under the Securities Act may be required on the part of any such selling holder
or any such controlling person in circumstances for which indemnification is
provided under this Section 9; then, and in

                                      11

<PAGE>

each such case, the Company and such holder will contribute to the aggregate 
losses, claims, damages or liabilities to which they may be subject (after 
contribution from others) as is appropriate to reflect the relative fault of 
the Company and such holder in connection with the statements or omissions 
which resulted in such losses, claims, damages or liabilities, as well as the 
relative benefit received by the Company and such holder as a result of the 
offering in question, it being understood that the parties acknowledge that 
the overriding equitable consideration to be given effect in connection with 
this provision is the ability of one party or the other to correct the 
statement or omission which resulted in such losses, claims, damages or 
liabilities, and that it would not be just and equitable if contribution 
pursuant hereto were to be determined by pro rata allocation or by any other 
method of allocation which does not take into consideration the foregoing 
equitable considerations; provided, however, that, in any such case, (A) no 
such holder will be required to contribute any amount in excess of the public 
offering price of all such Restricted Stock offered by it pursuant to such 
registration statement; and (B) no person or entity guilty of fraudulent 
misrepresentation (within the meaning of Section 11(f) of the Securities Act) 
will be entitled to contribution from any person or entity who was not guilty 
of such fraudulent misrepresentation.

         10.  Removal of Legends, Etc.  Notwithstanding the foregoing
provisions of Sections 2 through 9 hereof, the restrictions imposed by Sections
2 through 9 on the transferability of any Preferred Shares, Conversion Shares,
Warrant Shares and Perkin-Elmer Shares shall cease and terminate when (a) any
such Preferred Shares, Perkin-Elmer Shares, Conversion Shares or Warrant Shares
are sold or otherwise disposed of in accordance with the intended method of
disposition by the seller or sellers thereof set forth in a registration
statement or such other method contemplated by Section 3 hereof that does not
require that the securities transferred bear the legend set forth in Section 2
hereof, or (b) the holder of such Preferred Shares, Perkin-Elmer Shares,
Conversion Shares or Warrant Shares has met the requirements for transfer
pursuant to subparagraph (k) of Rule 144 (as amended from time to time)
promulgated by the Commission under the Securities Act.  Whenever the
restrictions imposed by Sections 2 through 9 hereof have terminated, a holder of
a certificate for such Preferred Shares, Perkin-Elmer Shares, Conversion Shares
or Warrant Shares as to which such restrictions have terminated shall be
entitled to receive from the Company, without expense, a new certificate not
bearing the restrictive legend set forth in Section 2 hereof and not containing
any other reference to the restrictions imposed by this Agreement.

                                      12

<PAGE>

         11.  Changes in Common Stock or Preferred Stock.  If, and as often as,
there is any change in the Common Stock or the Preferred Stock by way of a stock
split, stock dividend, combination or reclassification, or through a merger,
consolidation, reorganization or recapitalization, or by any other means,
appropriate adjustment shall be made in the provisions hereof so that the rights
and privileges granted hereby shall continue with respect to the Common Stock or
the Preferred Stock as so changed.

         12.  Rule 144 Reporting.  With a view to making available the benefits
of certain rules and regulations of the Commission which may at any time permit
the sale of the Restricted Stock to the public without registration, at all
times the Company agrees to:

              (a)  make and keep public information available, as those terms
are understood and defined in Rule 144 under the Securities Act;

              (b)  use all reasonable efforts to file with the Commission in a
timely manner all reports and other documents required of the Company under the
Securities Act and the Exchange Act; and

              (c)  furnish to each holder of Restricted Stock forthwith upon
request a written statement by the Company as to its compliance with the
reporting requirements of such Rule 144 and of the Securities Act and the
Exchange Act, a copy of the most recent annual or quarterly report of the
Company, and such other reports and documents so filed by the Company as such
holder may reasonably request in availing itself of any rule or regulation of
the Commission allowing such holder to sell any Restricted Stock without
registration.

         13.  Representations and Warranties of the Company.  The Company
represents and warrants to each of the Original Holders as follows:

              (a)  The execution, delivery and performance of this Agreement by
the Company have been duly authorized by all requisite corporate action and will
not violate any provision of law, any order of any court or other agency of
government, the Charter or By-laws of the Company or its subsidiaries or any
provision of any indenture, agreement or other instrument to which it or its
subsidiaries or any or their properties or assets is bound, or conflict with,
result in a breach of or constitute (with due notice or lapse of time or both) a
default under any such indenture, agreement or other instrument or result in the
creation or imposition of any lien, charge or encumbrance of any

                                      13

<PAGE>

nature whatsoever upon any of the properties or assets of the Company or its 
subsidiaries.

              (b)  This Agreement has been duly executed and delivered by the
Company and constitutes the legal, valid and binding obligation of the Company,
enforceable in accordance with its terms.

         14.  Miscellaneous.

              (a)   All covenants and agreements contained in this Agreement by
or on behalf of any of the parties hereto shall bind and inure to the benefit of
the respective successors and assigns of the parties hereto (including without
limitation transferees of any Preferred Shares or Restricted Stock), whether so
expressed or not, provided, however, that registration rights conferred herein
on the holders of Preferred Shares, Perkin-Elmer Shares, Warrants, or Restricted
Stock, shall only inure to the benefit of a transferee of Preferred Shares,
Perkin-Elmer Shares, Warrants, or Restricted Stock, if (i) there is transferred
to such transferee at least 20% of the total shares of Restricted Stock
originally issued pursuant to the Merger Agreement to the direct or indirect
transferor of such transferee or (ii) such transferee is a partner, shareholder
or affiliate of a party hereto.

              (b)  All notices, requests, consents and other communications
hereunder shall be in writing and shall be mailed by certified or registered
mail, return receipt requested, postage prepaid, or telexed, in the case of
non-U.S. residents, addressed as follows:

                   if to the Company, at:

                   Strategic Diagnostics Inc.
                   128 Sandy Drive
                   Newark, DE 19713-1147
                   Attn: President

                   if to any Original Holder, at the most recent address given
by such party to the Company;

                   if to any subsequent holder of Preferred Shares,
Perkin-Elmer Shares, Warrants, or Restricted Stock, to it at such address as may
have been furnished to the Company in writing by such holder;

or, in any case, at such other address or addresses as shall have been furnished
in writing to the Company (in the case of a holder of Preferred Shares,
Perkin-Elmer Shares or Restricted Stock) or

                                      14

<PAGE>

to the holders of Preferred Shares, Perkin-Elmer Shares or Restricted Stock 
(in the case of the Company) in accordance with the provisions of this 
paragraph.

              (c)  This Agreement shall be governed by and construed in
accordance with the laws of the State of Delaware.

              (d)  This Agreement may not be amended or modified, and no
provision hereof may be waived, without the written consent of the Company and
the holders of at least two-thirds of the outstanding shares of Restricted
Stock.  In addition, the Agreement may not be amended in a manner that is
materially adverse to the rights of the parties hereunder without the written
consent of the holders of at least a majority of the outstanding shares of
Restricted Stock. 

              (e)  This Agreement may be executed in two or more counterparts,
each of which shall be deemed an original, but all of which together shall
constitute one and the same instrument.

              (f)  The obligations of the Company to register shares of
Restricted Stock under Sections 4 or 5 shall terminate on the fifth anniversary
of the date of this Agreement.

              (g)  Notwithstanding the provisions of Section 6(a), the
Company's obligation to file a registration statement, or cause such
registration statement to become and remain effective, shall be suspended for a
period not to exceed 90 days in any 12-month period if there exists at the time
material non-public information relating to the Company which, in the reasonable
opinion of the Company, should not be disclosed.

              (h)  From the date of this Agreement, the Company shall not grant
to any third party any registration rights more favorable than any of those
contained herein, so long as any of the registration rights under this Agreement
remains in effect.

              (i)  If any provision of this Agreement shall be held to be
illegal, invalid or unenforceable, such illegality, invalidity or
unenforceability shall attach only to such provision and shall not in any manner
affect or render illegal, invalid or unenforceable any other provision of this
Agreement, and this Agreement shall be carried out as if any such illegal,
invalid or unenforceable provision were not contained herein.

                  [REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                      15

<PAGE>


         Please indicate your acceptance of the foregoing by signing and
returning the enclosed counterpart of this letter, whereupon this Agreement
shall be a binding agreement between the Company and you.

                                  Very truly yours,

                                  ENSYS ENVIRONMENTAL
                                  PRODUCTS, INC.


                                  By: /s/Grover C. Wrenn
                                      -----------------------------
                                      Title: President and Chief
                                             Executive Officer


AGREED TO AND ACCEPTED as of
the date first above written.


DSV PARTNERS IV

By: DSV Management, Ltd.,
    its general partner

By:  /s/Mort Collins
     ----------------------------
     General Partner


EDISON VENTURE FUND II, L.P.

By: Edison Partners II, L.P.,
    General Partner

By:  /s/Richard J. Defieux
     ----------------------------
    General Partner


EDISON VENTURE FUND II-PA, L.P.

By: Edison Partners II, L.P.,
    General Partner

By:  /s/Richard J. Defieux    
     ----------------------------
    General Partner


THE PERKIN-ELMER CORPORATION


By:  /s/Stephen O. Jaeger     
     ----------------------------

<PAGE>

                                                                      EXHIBIT 3

                                          COMMON STOCK WARRANT NO. W-12/30/96-A

    THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "ACT"), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE
SOLD OR TRANSFERRED UNLESS SUCH SALE OR TRANSFER IS IN ACCORDANCE WITH THE
REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS OR SOME OTHER
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS IS
AVAILABLE WITH RESPECT THERETO.


                          ENSYS ENVIRONMENTAL PRODUCTS, INC.
                                 WARRANT TO PURCHASE
                                     COMMON STOCK


    1. Issuance.  This Warrant is issued to DSV Partners IV, L.P., by EnSys
Environmental Products, Inc., a Delaware corporation (referred to hereinafter,
with its successors, as the "Company"), on this 30th day of December, 1996 (the
"Warrant Issuance Date"), in consideration of the surrender to the Company for
cancellation of certain warrants to purchase common stock of Strategic
Diagnostics Inc., which warrants were issued on June 23, 1993.

    2. Purchase Price; Number of Shares. Subject to the terms and conditions
hereinafter set forth, the registered holder of this Warrant (the "Holder") is
entitled upon surrender of this Warrant with the subscription form annexed
hereto, duly executed, at the office of the Company, to purchase 58,635 shares
of common stock of the Company, par value $.01 per share (the "Common Stock"),
at the per share exercise price of $2.24 (the "Purchase Price").

    3. Payment of Purchase Price.  The Purchase Price may be paid (i) in cash
or by check, (ii) by the surrender by the Holder to the Company of any
promissory notes or other obligations issued by the Company, with all such notes
and obligations so surrendered being credited against the Purchase Price in an
amount equal to the principal amount thereof plus accrued interest to the date
of surrender, (iii) through delivery by the Holder to the Company of other
securities issued by the Company, with such securities being credited against
the Purchase Price in an amount equal to the fair market value thereof, as
determined in good faith by the Board of Directors of the Company (the "Board"),
or (iv) by any combination of the foregoing.  The Board shall promptly respond
in writing to an inquiry by the Holder as to the fair market value of any
securities the Holder may wish to deliver to the Company pursuant to clause
(iii) above.

    4. Net Issue Election.  The Holder may elect to receive, without the
payment by the Holder of any additional consideration, shares equal to the value
of this Warrant or any portion hereof by the surrender of this Warrant or such
portion to the Company, with the net issue election notice annexed hereto duly
executed, at the office of the Company; PROVIDED, that the


<PAGE>

Holder may not make such an election unless (i) the Company has registered 
its securities pursuant to the Securities Act of 1933, as amended, (the 
"Act") or in connection with such registration or (ii) upon the expiration of 
this Warrant.  Thereupon, the Company shall issue to the Holder such number 
of fully paid and nonassessable shares of Common Stock as is computed using 
the following formula:

                                       X = Y(A-B)
                                           ------
                                             A

where X = the number of shares to be issued to the Holder pursuant to this
Section 4.

    Y = the number of shares covered by this Warrant in respect of which the
net issue election is made pursuant to this Section 4.

    A = the fair market value of one share of Common Stock.  If the Company's 
securities are registered pursuant to the Act, the fair market value shall 
mean the average high and low prices of the Common Stock on the day prior to 
the exercise of this Warrant, if the Common Stock is being traded on a 
national exchange; or the last reported sale price on the day prior to 
exercise of this Warrant, if the Common Stock is traded on the Nasdaq 
National Market, and if the Common Stock is not traded on a national 
exchange; or the closing bid price (or average of bid prices) last quoted on 
the day prior to the exercise of this Warrant by an established quotation 
service for over-the-counter securities, if the Common Stock is not reported 
on the Nasdaq National Market or a national exchange.  If the election occurs 
in connection with the registration of securities, then the fair market value 
shall be the price offered to the public. Otherwise, the fair market value 
shall be as determined in good faith by the Board, at the time the net issue 
election is made pursuant to this Section 4.

    B = the Purchase Price in effect under this Warrant at the time the net
issue election is made pursuant to this Section 4.

The Board shall promptly respond in writing to an inquiry by the Holder as to
the fair market value of one share of Common Stock.

    5. Partial Exercise.  This Warrant may be exercised in part, and the Holder
shall be entitled to receive a new warrant, which shall be dated as of the date
of this Warrant, covering the number of shares in respect of which this Warrant
shall not have been exercised.

    6. Issuance Date.  The person or persons in whose name or names any
certificate representing shares of Common Stock is issued hereunder shall be
deemed to have become the holder of record of the shares represented thereby as
at the close of business on the date this Warrant is exercised with respect to
such shares, whether or not the transfer books of the Company shall be closed.

                                  2

<PAGE>

    7. Expiration Date.  This Warrant shall expire at the close of business on
June 23, 1998, and shall be void thereafter.

    8. Reserved Shares; Valid Issuance.  The Company covenants that it will at
all times from and after the date hereof reserve and keep available such number
of its authorized shares of Common Stock, free from all preemptive or similar
rights therein, as will be sufficient to permit the exercise of this Warrant in
full.  The Company further covenants that, assuming the receipt by the Company
of the consideration therefor, such shares as may be issued pursuant to the
exercise of this Warrant will, upon issuance, be duly and validly issued, fully
paid and nonassessable and free from all taxes, liens and charges with respect
to the issuance thereof.

    9. Dividends.  If at any time after the Warrant Issuance Date, the Company
subdivides the Common Stock, by split-up or otherwise, or combines the Common
Stock, or issues additional shares of Common Stock in payment of a stock
dividend on the Common Stock, the number of shares issuable on the exercise of
this Warrant shall forthwith be proportionately increased in the case of a
subdivision or stock dividend, or proportionately decreased in the case of a
combination, and the Purchase Price shall forthwith be proportionately decreased
in the case of a subdivision or stock dividend, or proportionately increased in
the case of a combination.  Whenever the Purchase Price is adjusted, as herein
provided, the Company shall promptly deliver to the Holder a certificate of an
officer of the Company setting forth the Purchase Price after such adjustment
and setting forth a brief statement on the facts requiring such adjustment.

    10. Mergers and Reclassifications.  If at any time after the Warrant
Issuance Date there shall be any reclassification, capital reorganization or
change of the Common Stock (other than as a result of a subdivision, combination
or stock dividend provided for in Section 9 hereof), or any consolidation of the
Company with, or merger of the Company into, another corporation or other
business organization (other than a consolidation or merger in which the Company
is the continuing corporation and which does not result in any reclassification
or change of the outstanding Common Stock), or any sale or conveyance to another
corporation or other business organization of all or substantially all of the
assets of the Company, then, as a condition of such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, lawful
provisions shall be made, and duly executed documents evidencing the same from
the Company or its successor shall be delivered to the Holder, so that the
Holder shall thereafter have the right to purchase, at a total price not to
exceed that payable upon the exercise of this Warrant in full, the kind and
amount of shares of stock and other securities and property receivable upon such
reclassification, reorganization, change, consolidation, merger, sale or
conveyance by a holder of the number of shares of Common Stock which might have
been purchased by the Holder immediately prior to such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, and in any
such case appropriate provisions shall be made with respect to the rights and
interest of the Holder to the end that the provisions hereof (including without
limitation, provisions for the adjustment of the Purchase Price and the number
of shares issuable hereunder) shall thereafter be applicable in relation to any
shares of stock or other securities and property thereafter deliverable upon
exercise hereof.

                                    3

<PAGE>

    11. Fractional Shares.  In no event shall any fractional share of Common
Stock be issued upon any exercise of this Warrant.

    12. Notices of Record Date, Etc.  In the event of:

         (a) any taking by the Company of a record of the holders of any class
of securities for the purpose of determining the holders thereof who are
entitled to receive any dividend or other distribution, or any right to
subscribe for, purchase or otherwise acquire any shares of stock of any class or
any other securities or property, or to receive any other right,

         (b) any reclassification of the capital stock of the Company, capital
reorganization of the Company, consolidation or merger involving the Company, or
sale or conveyance of all or substantially all of its assets, or 

         (c) any voluntary or involuntary dissolution, liquidation or
winding-up of the Company,

then and in each such event the Company will mail or cause to be mailed to the
Holder a notice specifying (i) the date on which any such record is to be taken
for the purpose of such dividend, distribution or right, and stating the amount
and character of such dividend, distribution or right, or (ii) the date on which
any such reclassification, reorganization, consolidation, merger, sale or
conveyance, dissolution, liquidation or winding-up is to take place, and the
time, if any is to be fixed, as of which the holders of record in respect of
such event are to be determined.  Such notice shall be mailed at least 20 days
prior to the date specified in such notice on which any such action is to be
taken.

    13. Amendment.  The terms of this Warrant may be amended, modified or
waived only by written agreement of the Company and the Holder.

    14. Warrant Register Transfer, Etc.

              A. The Company will maintain a register containing the names and
addresses of the registered holders of outstanding Warrants.  The Holder may
change its address as shown on the warrant register by written notice to the
Company requesting such change.  Any notice or written communication required or
permitted to be given to the Holder may be given by certified mail or delivered
to the Holder at its address as shown on the warrant register.

              B. This Warrant may not be transferred or assigned in whole or in
part by the Holder without the prior written consent of the Company, which
consent shall not be unreasonably withheld (it being understood that the Company
may withhold consent to any transfer of the Warrant to any person seeking to
obtain control of the Company), except that prior written consent of the Company
will not be required for a transfer of the Warrant in whole by the

                                   4

<PAGE>

Holder to an "affiliate" of the Holder.  An "affiliate" of the Holder shall 
mean any other person or entity directly or indirectly controlling, 
controlled by or under direct or indirect common control with the Holder.  
Prior to and as a condition to effecting any such transfer the Holder shall 
deliver to the Company an opinion of counsel reasonably satisfactory to the 
Company to the effect that such transfer will comply with all applicable 
securities laws.

              C. In case this Warrant shall be mutilated, lost, stolen or
destroyed, the Company shall issue a new warrant of like tenor and denomination
and deliver the same (i) in exchange and substitution for and upon surrender and
cancellation of any mutilated Warrant, or (ii) in lieu of any Warrant lost,
stolen or destroyed, upon receipt of evidence reasonably satisfactory to the
Company of the loss, theft or destruction of such Warrant (including a
reasonably detailed affidavit with respect to the circumstances of any loss,
theft or destruction) and of indemnity reasonably satisfactory to the Company.

    15. No Impairment.  The Company will not, by amendment of its Certificate
of Incorporation or through any reclassification, capital reorganization,
consolidation, merger, sale or conveyance of assets, dissolution, liquidation,
issue or sale of securities or any other voluntary action, avoid or seek to
avoid the observance or performance of any of the terms of this Warrant, but
will at all times in good faith assist in the carrying out of all such terms and
in the taking of all such action as may be necessary or appropriate in order to
protect the rights of the Holder.

    16. Governing Law.  The provisions and terms of this Warrant shall be
governed by and construed in accordance with the internal laws of the State of
Delaware.

    17. Successors and Assigns.  This Warrant shall be binding upon the
Company's successors and assigns and shall inure to the benefit of the Holder's
successors, legal representatives and permitted assigns.

    18. Business Days.  If the last or appointed day for the taking of any
action required or the expiration of any right granted herein shall be a
Saturday or Sunday or a legal holiday in Delaware, then such action may be taken
or right may be exercised on the next succeeding day which is not a Saturday or
Sunday or such a legal holiday.

                                    5

<PAGE>

    IN WITNESS WHEREOF, the Company has caused this Warrant to be executed by
its duly authorized officer, under seal, as of the date above written.

                        ENSYS ENVIRONMENTAL PRODUCTS, INC.

                        By: /s/ Grover C. Wrenn
                           -----------------------------------------
                        Title: President and Chief Executive Officer 


                                    6

<PAGE>

                                     SUBSCRIPTION


To:___________________________         Date:____________________________


    The undersigned hereby subscribes for _________________ shares of Common
Stock covered by this Warrant.  The certificate(s) for such shares shall be
issued in the name of the undersigned or as otherwise indicated below:

                                  Signature ________________________________


                                  Name for Registration_____________________


                                  Mailing Address___________________________

                                  __________________________________________

                                    7

<PAGE>
 
                              NET ISSUE ELECTION NOTICE


To:____________________________        Date:________________________

    The undersigned hereby elects under Section 4 to surrender the right to
purchase ___________ shares of Common Stock Pursuant to this Warrant.  The
certificate(s) for the shares issuable upon such net issue election shall be
issued in the name of the undersigned or as otherwise indicated below.

                                  Signature_________________________________


                                  Name for Registration_____________________


                                  Mailing Address___________________________

                                  __________________________________________

                                    8

<PAGE>




                                         COMMON STOCK WARRANT NO. W-12/30/96-B

    THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS 
AMENDED (THE "ACT"), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE 
SOLD OR TRANSFERRED UNLESS SUCH SALE OR TRANSFER IS IN ACCORDANCE WITH THE 
REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS OR SOME OTHER 
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS 
IS AVAILABLE WITH RESPECT THERETO.

                          ENSYS ENVIRONMENTAL PRODUCTS, INC.
                                 WARRANT TO PURCHASE
                                     COMMON STOCK


     1. Issuance.  This Warrant is issued to DSV Partners IV, L.P., by EnSys 
Environmental Products, Inc., a Delaware corporation (referred to 
hereinafter, with its successors, as the "Company"), on this 30th day of 
December, 1996 (the "Warrant Issuance Date"), in consideration of the 
surrender to the Company for cancellation of certain warrants to purchase 
common stock of Strategic Diagnostics Inc., which warrants were issued on 
October 27, 1994.

     2. Purchase Price; Number of Shares. Subject to the terms and conditions 
hereinafter set forth, the registered holder of this Warrant (the "Holder") 
is entitled upon surrender of this Warrant with the subscription form annexed 
hereto, duly executed, at the office of the Company, to purchase 22,337 
shares of common stock of the Company, par value $.01 per share (the "Common 
Stock"), at the per share exercise price of $2.24 (the "Purchase Price").

     3. Payment of Purchase Price.  The Purchase Price may be paid (i) in 
cash or by check, (ii) by the surrender by the Holder to the Company of any 
promissory notes or other obligations issued by the Company, with all such 
notes and obligations so surrendered being credited against the Purchase 
Price in an amount equal to the principal amount thereof plus accrued 
interest to the date of surrender, (iii) through delivery by the Holder to 
the Company of other securities issued by the Company, with such securities 
being credited against the Purchase Price in an amount equal to the fair 
market value thereof, as determined in good faith by the Board of Directors 
of the Company (the "Board"), or (iv) by any combination of the foregoing.  
The Board shall promptly respond in writing to an inquiry by the Holder as to 
the fair market value of any securities the Holder may wish to deliver to the 
Company pursuant to clause (iii) above.

     4. Net Issue Election.  The Holder may elect to receive, without the 
payment by the Holder of any additional consideration, shares equal to the 
value of this Warrant or any portion hereof by the surrender of this Warrant 
or such portion to the Company, with the net issue election notice annexed 
hereto duly executed, at the office of the Company; provided, that the Holder 
may not make such an election unless (i) the Company has registered its 
securities pursuant to the Securities Act of 1933, as amended, (the "Act") or 
in connection with such registration or (ii) upon the expiration of this 
Warrant.  Thereupon, the Company shall issue to the Holder such number of 
fully paid and nonassessable shares of Common Stock as is computed using the 
following formula:

<PAGE>

                                     X = Y(A-B)
                                         ------ 
                                           A

where X = the number of shares to be issued to the Holder pursuant to this 
Section 4.

      Y = the number of shares covered by this Warrant in respect of which 
the net issue election is made pursuant to this Section 4.

      A = the fair market value of one share of Common Stock.  If the 
Company's securities are registered pursuant to the Act, the fair market 
value shall mean the average high and low prices of the Common Stock on the 
day prior to the exercise of this Warrant, if the Common Stock is being 
traded on a national exchange; or the last reported sale price on the day 
prior to exercise of this Warrant, if the Common Stock is traded on the 
Nasdaq National Market, and if the Common Stock is not traded on a national 
exchange; or the closing bid price (or average of bid prices) last quoted on 
the day prior to the exercise of this Warrant by an established quotation 
service for over-the-counter securities, if the Common Stock is not reported 
on the Nasdaq National Market or a national exchange.  If the election occurs 
in connection with the registration of securities, then the fair market value 
shall be the price offered to the public.  Otherwise, the fair market value 
shall be as determined in good faith by the Board, at the time the net issue 
election is made pursuant to this Section 4.

      B = the Purchase Price in effect under this Warrant at the time the
net issue election is made pursuant to this Section 4.

The Board shall promptly respond in writing to an inquiry by the Holder as to
the fair market value of one share of Common Stock.

     5. Partial Exercise.  This Warrant may be exercised in part, and the
Holder shall be entitled to receive a new warrant, which shall be dated as of
the date of this Warrant, covering the number of shares in respect of which this
Warrant shall not have been exercised.

     6. Issuance Date.  The person or persons in whose name or names any
certificate representing shares of Common Stock is issued hereunder shall be
deemed to have become the holder of record of the shares represented thereby as
at the close of business on the date this Warrant is exercised with respect to
such shares, whether or not the transfer books of the Company shall be closed.

     7. Expiration Date.  This Warrant shall expire at the close of
business on October 27, 1999, and shall be void thereafter.

     8. Reserved Shares; Valid Issuance.  The Company covenants that it will 
at all times from and after the date hereof reserve and keep available such 
number of its authorized shares of Common Stock, free from all preemptive or 
similar rights therein, as will be sufficient to permit the exercise of this 
Warrant in full.  The Company further covenants that, assuming the receipt by 

                                     2

<PAGE>

the Company of the consideration therefor, such shares as may be issued 
pursuant to the exercise of this Warrant will, upon issuance, be duly and 
validly issued, fully paid and nonassessable and free from all taxes, liens 
and charges with respect to the issuance thereof.

     9. Dividends.  If at any time after the Warrant Issuance Date, the
Company subdivides the Common Stock, by split-up or otherwise, or combines the
Common Stock, or issues additional shares of Common Stock in payment of a stock
dividend on the Common Stock, the number of shares issuable on the exercise of
this Warrant shall forthwith be proportionately increased in the case of a
subdivision or stock dividend, or proportionately decreased in the case of a
combination, and the Purchase Price shall forthwith be proportionately decreased
in the case of a subdivision or stock dividend, or proportionately increased in
the case of a combination.  Whenever the Purchase Price is adjusted, as herein
provided, the Company shall promptly deliver to the Holder a certificate of an
officer of the Company setting forth the Purchase Price after such adjustment
and setting forth a brief statement on the facts requiring such adjustment.

     10. Mergers and Reclassifications.  If at any time after the Warrant
Issuance Date there shall be any reclassification, capital reorganization or
change of the Common Stock (other than as a result of a subdivision, combination
or stock dividend provided for in Section 9 hereof), or any consolidation of the
Company with, or merger of the Company into, another corporation or other
business organization (other than a consolidation or merger in which the Company
is the continuing corporation and which does not result in any reclassification
or change of the outstanding Common Stock), or any sale or conveyance to another
corporation or other business organization of all or substantially all of the
assets of the Company, then, as a condition of such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, lawful
provisions shall be made, and duly executed documents evidencing the same from
the Company or its successor shall be delivered to the Holder, so that the
Holder shall thereafter have the right to purchase, at a total price not to
exceed that payable upon the exercise of this Warrant in full, the kind and
amount of shares of stock and other securities and property receivable upon such
reclassification, reorganization, change, consolidation, merger, sale or
conveyance by a holder of the number of shares of Common Stock which might have
been purchased by the Holder immediately prior to such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, and in any
such case appropriate provisions shall be made with respect to the rights and
interest of the Holder to the end that the provisions hereof (including without
limitation, provisions for the adjustment of the Purchase Price and the number
of shares issuable hereunder) shall thereafter be applicable in relation to any
shares of stock or other securities and property thereafter deliverable upon
exercise hereof.

     11. Fractional Shares.  In no event shall any fractional share of
Common Stock be issued upon any exercise of this Warrant.

     12. Notices of Record Date, Etc.  In the event of:

         (a) any taking by the Company of a record of the holders of any 
class of securities for the purpose of determining the holders thereof who 
are entitled to receive any 

                                     3

<PAGE>

dividend or other distribution, or any right to subscribe for, purchase or 
otherwise acquire any shares of stock of any class or any other securities or 
property, or to receive any other right,

         (b) any reclassification of the capital stock of the Company,
capital reorganization of the Company, consolidation or merger involving the
Company, or sale or conveyance of all or substantially all of its assets, or

         (c) any voluntary or involuntary dissolution, liquidation or
winding-up of the Company,

then and in each such event the Company will mail or cause to be mailed to the
Holder a notice specifying (i) the date on which any such record is to be taken
for the purpose of such dividend, distribution or right, and stating the amount
and character of such dividend, distribution or right, or (ii) the date on which
any such reclassification, reorganization, consolidation, merger, sale or
conveyance, dissolution, liquidation or winding-up is to take place, and the
time, if any is to be fixed, as of which the holders of record in respect of
such event are to be determined.  Such notice shall be mailed at least 20 days
prior to the date specified in such notice on which any such action is to be
taken.

     13. Amendment.  The terms of this Warrant may be amended, modified or
waived only by written agreement of the Company and the Holder.

     14. Warrant Register Transfer, Etc.

              A. The Company will maintain a register containing the names 
and addresses of the registered holders of outstanding Warrants.  The Holder 
may change its address as shown on the warrant register by written notice to 
the Company requesting such change.  Any notice or written communication 
required or permitted to be given to the Holder may be given by certified 
mail or delivered to the Holder at its address as shown on the warrant 
register.

              B. This Warrant may not be transferred or assigned in whole or 
in part by the Holder without the prior written consent of the Company, which 
consent shall not be unreasonably withheld (it being understood that the 
Company may withhold consent to any transfer of the Warrant to any person 
seeking to obtain control of the Company), except that prior written consent 
of the Company will not be required for a transfer of the Warrant in whole by 
the Holder to an "affiliate" of the Holder.  An "affiliate" of the Holder 
shall mean any other person or entity directly or indirectly controlling, 
controlled by or under direct or indirect common control with the Holder.  
Prior to and as a condition to effecting any such transfer the Holder shall 
deliver to the Company an opinion of counsel reasonably satisfactory to the 
Company to the effect that such transfer will comply with all applicable 
securities laws.

              C. In case this Warrant shall be mutilated, lost, stolen or 
destroyed, the Company shall issue a new warrant of like tenor and 
denomination and deliver the same (i) in exchange and substitution for and 
upon surrender and cancellation of any mutilated Warrant, or 

                                     4

<PAGE>

(ii) in lieu of any Warrant lost, stolen or destroyed, upon receipt of 
evidence reasonably satisfactory to the Company of the loss, theft or 
destruction of such Warrant (including a reasonably detailed affidavit with 
respect to the circumstances of any loss, theft or destruction) and of 
indemnity reasonably satisfactory to the Company.

     15. No Impairment.  The Company will not, by amendment of its 
Certificate of Incorporation or through any reclassification, capital 
reorganization, consolidation, merger, sale or conveyance of assets, 
dissolution, liquidation, issue or sale of securities or any other voluntary 
action, avoid or seek to avoid the observance or performance of any of the 
terms of this Warrant, but will at all times in good faith assist in the 
carrying out of all such terms and in the taking of all such action as may be 
necessary or appropriate in order to protect the rights of the Holder.

     16. Governing Law.  The provisions and terms of this Warrant shall be 
governed by and construed in accordance with the internal laws of the State 
of Delaware.

     17. Successors and Assigns.  This Warrant shall be binding upon the 
Company's successors and assigns and shall inure to the benefit of the 
Holder's successors, legal representatives and permitted assigns.

     18. Business Days.  If the last or appointed day for the taking of any 
action required or the expiration of any right granted herein shall be a 
Saturday or Sunday or a legal holiday in Delaware, then such action may be 
taken or right may be exercised on the next succeeding day which is not a 
Saturday or Sunday or such a legal holiday.


                                     5

<PAGE>

     IN WITNESS WHEREOF, the Company has caused this Warrant to be executed
by its duly authorized officer, under seal, as of the date above written.

                             ENSYS ENVIRONMENTAL PRODUCTS, INC.

                             By: /s/ Grover C. Wrenn
                                 ________________________________________

                             Title: President and Chief Executive Officer 
                                    _____________________________________

                                     6

<PAGE>

                                 SUBSCRIPTION


To: ______________________________             Date: ________________________


         The undersigned hereby subscribes for _______________ shares of 
Common Stock covered by this Warrant.  The certificate(s) for such shares 
shall be issued in the name of the undersigned or as otherwise indicated 
below:

                                       Signature _____________________________


                                       Name for Registration _________________


                                       Mailing Address _______________________

                                       _______________________________________


                                     7

<PAGE>

                                                                             
                          NET ISSUE ELECTION NOTICE

To: ______________________________             Date: ________________________

         The undersigned hereby elects under Section 4 to surrender the right
to purchase ___________ shares of Common Stock Pursuant to this Warrant.  The
certificate(s) for the shares issuable upon such net issue election shall be
issued in the name of the undersigned or as otherwise indicated below.

                                       Signature _____________________________


                                       Name for Registration _________________


                                       Mailing Address _______________________

                                       _______________________________________



                                     8

<PAGE>



                                           COMMON STOCK WARRANT NO. W-12/30/96-C

    THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "ACT"), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE
SOLD OR TRANSFERRED UNLESS SUCH SALE OR TRANSFER IS IN ACCORDANCE WITH THE
REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS OR SOME OTHER
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS IS
AVAILABLE WITH RESPECT THERETO.


                          ENSYS ENVIRONMENTAL PRODUCTS, INC.
                                 WARRANT TO PURCHASE
                                     COMMON STOCK


         1. Issuance.  This Warrant is issued to DSV Partners IV, L.P., by
EnSys Environmental Products, Inc., a Delaware corporation (referred to
hereinafter, with its successors, as the "Company"), on this 30th day of
December, 1996 (the "Warrant Issuance Date"), in consideration of the surrender
to the Company for cancellation of certain warrants to purchase common stock of
Strategic Diagnostics Inc., which warrants were issued on January 2, 1995.

         2. Purchase Price; Number of Shares. Subject to the terms and
conditions hereinafter set forth, the registered holder of this Warrant (the
"Holder") is entitled upon surrender of this Warrant with the subscription form
annexed hereto, duly executed, at the office of the Company, to purchase 11,169
shares of common stock of the Company, par value $.01 per share (the "Common
Stock"), at the per share exercise price of $2.24 (the "Purchase Price").

         3. Payment of Purchase Price.  The Purchase Price may be paid (i) in
cash or by check, (ii) by the surrender by the Holder to the Company of any
promissory notes or other obligations issued by the Company, with all such notes
and obligations so surrendered being credited against the Purchase Price in an
amount equal to the principal amount thereof plus accrued interest to the date
of surrender, (iii) through delivery by the Holder to the Company of other
securities issued by the Company, with such securities being credited against
the Purchase Price in an amount equal to the fair market value thereof, as
determined in good faith by the Board of Directors of the Company (the "Board"),
or (iv) by any combination of the foregoing.  The Board shall promptly respond
in writing to an inquiry by the Holder as to the fair market value of any
securities the Holder may wish to deliver to the Company pursuant to clause
(iii) above.

         4. Net Issue Election.  The Holder may elect to receive, without the
payment by the Holder of any additional consideration, shares equal to the value
of this Warrant or any portion hereof by the surrender of this Warrant or such
portion to the Company, with the net issue election notice annexed hereto duly
executed, at the office of the Company; PROVIDED, that the Holder may not make
such an election unless (i) the Company has registered its securities pursuant
to the Securities Act of 1933, as amended, (the "Act") or in connection with
such registration or (ii) upon the expiration of this Warrant.  Thereupon, the
Company shall issue to 





<PAGE>


the Holder such number of fully paid and nonassessable shares of Common Stock
as is computed using the following formula:

                                       X=Y(A-B)
                                         ------
                                          A

where X = the number of shares to be issued to the Holder pursuant to this
Section 4.

         Y = the number of shares covered by this Warrant in respect of which
the net issue election is made pursuant to this Section 4.

         A = the fair market value of one share of Common Stock.  If the
Company's securities are registered pursuant to the Act, the fair market value
shall mean the average high and low prices of the Common Stock on the day prior
to the exercise of this Warrant, if the Common Stock is being traded on a
national exchange; or the last reported sale price on the day prior to exercise
of this Warrant, if the Common Stock is traded on the Nasdaq National Market,
and if the Common Stock is not traded on a national exchange; or the closing bid
price (or average of bid prices) last quoted on the day prior to the exercise of
this Warrant by an established quotation service for over-the-counter
securities, if the Common Stock is not reported on the Nasdaq National Market or
a national exchange.  If the election occurs in connection with the registration
of securities, then the fair market value shall be the price offered to the
public.  Otherwise, the fair market value shall be as determined in good faith
by the Board, at the time the net issue election is made pursuant to this
Section 4.

         B = the Purchase Price in effect under this Warrant at the time the
net issue election is made pursuant to this Section 4.

The Board shall promptly respond in writing to an inquiry by the Holder as to
the fair market value of one share of Common Stock.

         5. Partial Exercise.  This Warrant may be exercised in part, and the
Holder shall be entitled to receive a new warrant, which shall be dated as of
the date of this Warrant, covering the number of shares in respect of which this
Warrant shall not have been exercised.

         6. Issuance Date.  The person or persons in whose name or names any
certificate representing shares of Common Stock is issued hereunder shall be
deemed to have become the holder of record of the shares represented thereby as
at the close of business on the date this Warrant is exercised with respect to
such shares, whether or not the transfer books of the Company shall be closed.

         7. Expiration Date.  This Warrant shall expire at the close of
business on January 2, 2000, and shall be void thereafter.

         8. Reserved Shares; Valid Issuance.  The Company covenants that it
will at all times


                                       2


<PAGE>


from and after the date hereof reserve and keep available such number of its
authorized shares of Common Stock, free from all preemptive or similar rights
therein, as will be sufficient to permit the exercise of this Warrant in full.
The Company further covenants that, assuming the receipt by the Company of the
consideration therefor, such shares as may be issued pursuant to the exercise
of this Warrant will, upon issuance, be duly and validly issued, fully paid and
nonassessable and free from all taxes, liens and charges with respect to the
issuance thereof.

         9. Dividends.  If at any time after the Warrant Issuance Date, the
Company subdivides the Common Stock, by split-up or otherwise, or combines the
Common Stock, or issues additional shares of Common Stock in payment of a stock
dividend on the Common Stock, the number of shares issuable on the exercise of
this Warrant shall forthwith be proportionately increased in the case of a
subdivision or stock dividend, or proportionately decreased in the case of a
combination, and the Purchase Price shall forthwith be proportionately decreased
in the case of a subdivision or stock dividend, or proportionately increased in
the case of a combination.  Whenever the Purchase Price is adjusted, as herein
provided, the Company shall promptly deliver to the Holder a certificate of an
officer of the Company setting forth the Purchase Price after such adjustment
and setting forth a brief statement on the facts requiring such adjustment.

         10. Mergers and Reclassifications.  If at any time after the Warrant
Issuance Date there shall be any reclassification, capital reorganization or
change of the Common Stock (other than as a result of a subdivision, combination
or stock dividend provided for in Section 9 hereof), or any consolidation of the
Company with, or merger of the Company into, another corporation or other
business organization (other than a consolidation or merger in which the Company
is the continuing corporation and which does not result in any reclassification
or change of the outstanding Common Stock), or any sale or conveyance to another
corporation or other business organization of all or substantially all of the
assets of the Company, then, as a condition of such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, lawful
provisions shall be made, and duly executed documents evidencing the same from
the Company or its successor shall be delivered to the Holder, so that the
Holder shall thereafter have the right to purchase, at a total price not to
exceed that payable upon the exercise of this Warrant in full, the kind and
amount of shares of stock and other securities and property receivable upon such
reclassification, reorganization, change, consolidation, merger, sale or
conveyance by a holder of the number of shares of Common Stock which might have
been purchased by the Holder immediately prior to such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, and in any
such case appropriate provisions shall be made with respect to the rights and
interest of the Holder to the end that the provisions hereof (including without
limitation, provisions for the adjustment of the Purchase Price and the number
of shares issuable hereunder) shall thereafter be applicable in relation to any
shares of stock or other securities and property thereafter deliverable upon
exercise hereof.

         11. Fractional Shares.  In no event shall any fractional share of
Common Stock be issued upon any exercise of this Warrant.

         12. Notices of Record Date, Etc.  In the event of:


                                       3


<PAGE>


              (a) any taking by the Company of a record of the holders of any
class of securities for the purpose of determining the holders thereof who are
entitled to receive any dividend or other distribution, or any right to
subscribe for, purchase or otherwise acquire any shares of stock of any class or
any other securities or property, or to receive any other right,

              (b) any reclassification of the capital stock of the Company,
capital reorganization of the Company, consolidation or merger involving the
Company, or sale or conveyance of all or substantially all of its assets, or

              (c) any voluntary or involuntary dissolution, liquidation or
winding-up of the Company,

then and in each such event the Company will mail or cause to be mailed to the
Holder a notice specifying (i) the date on which any such record is to be taken
for the purpose of such dividend, distribution or right, and stating the amount
and character of such dividend, distribution or right, or (ii) the date on which
any such reclassification, reorganization, consolidation, merger, sale or
conveyance, dissolution, liquidation or winding-up is to take place, and the
time, if any is to be fixed, as of which the holders of record in respect of
such event are to be determined.  Such notice shall be mailed at least 20 days
prior to the date specified in such notice on which any such action is to be
taken.

         13. Amendment.  The terms of this Warrant may be amended, modified or
waived only by written agreement of the Company and the Holder.

         14. Warrant Register Transfer, Etc.

                   A. The Company will maintain a register containing the names
and addresses of the registered holders of outstanding Warrants.  The Holder may
change its address as shown on the warrant register by written notice to the
Company requesting such change.  Any notice or written communication required or
permitted to be given to the Holder may be given by certified mail or delivered
to the Holder at its address as shown on the warrant register.

                   B. This Warrant may not be transferred or assigned in whole
or in part by the Holder without the prior written consent of the Company, which
consent shall not be unreasonably withheld (it being understood that the Company
may withhold consent to any transfer of the Warrant to any person seeking to
obtain control of the Company), except that prior written consent of the Company
will not be required for a transfer of the Warrant in whole by the Holder to an
"affiliate" of the Holder.  An "affiliate" of the Holder shall mean any other
person or entity directly or indirectly controlling, controlled by or under
direct or indirect common control with the Holder.  Prior to and as a condition
to effecting any such transfer the Holder shall deliver to the Company an
opinion of counsel reasonably satisfactory to the Company to the effect that
such transfer will comply with all applicable securities laws.


                                       4


<PAGE>


                   C. In case this Warrant shall be mutilated, lost, stolen or
destroyed, the Company shall issue a new warrant of like tenor and denomination
and deliver the same (i) in exchange and substitution for and upon surrender and
cancellation of any mutilated Warrant, or (ii) in lieu of any Warrant lost,
stolen or destroyed, upon receipt of evidence reasonably satisfactory to the
Company of the loss, theft or destruction of such Warrant (including a
reasonably detailed affidavit with respect to the circumstances of any loss,
theft or destruction) and of indemnity reasonably satisfactory to the Company.

         15. No Impairment.  The Company will not, by amendment of its
Certificate of Incorporation or through any reclassification, capital
reorganization, consolidation, merger, sale or conveyance of assets,
dissolution, liquidation, issue or sale of securities or any other voluntary
action, avoid or seek to avoid the observance or performance of any of the terms
of this Warrant, but will at all times in good faith assist in the carrying out
of all such terms and in the taking of all such action as may be necessary or
appropriate in order to protect the rights of the Holder.

         16. Governing Law.  The provisions and terms of this Warrant shall be
governed by and construed in accordance with the internal laws of the State of
Delaware.

         17. Successors and Assigns.  This Warrant shall be binding upon the
Company's successors and assigns and shall inure to the benefit of the Holder's
successors, legal representatives and permitted assigns.

         18. Business Days.  If the last or appointed day for the taking of any
action required or the expiration of any right granted herein shall be a
Saturday or Sunday or a legal holiday in Delaware, then such action may be taken
or right may be exercised on the next succeeding day which is not a Saturday or
Sunday or such a legal holiday.


                                       5


<PAGE>


         IN WITNESS WHEREOF, the Company has caused this Warrant to be executed
by its duly authorized officer, under seal, as of the date above written.

                             ENSYS ENVIRONMENTAL PRODUCTS, INC.

                             By: /s/ Grover C. Wrenn                            
                                 ----------------------------------------

                             Title: President and Chief Executive Officer
                                    -------------------------------------


                                       6


<PAGE>


                                     SUBSCRIPTION


To:___________________________         Date:____________________________


         The undersigned hereby subscribes for _________________ shares of
Common Stock covered by this Warrant.  The certificate(s) for such shares shall
be issued in the name of the undersigned or as otherwise indicated below:

                                       Signature _____________________________


                                       Name for Registration _________________


                                       Mailing Address _______________________

                                       _______________________________________


                                       7


<PAGE>


                              NET ISSUE ELECTION NOTICE


To:____________________________        Date:________________________

         The undersigned hereby elects under Section 4 to surrender the right
to purchase ___________ shares of Common Stock Pursuant to this Warrant.  The
certificate(s) for the shares issuable upon such net issue election shall be
issued in the name of the undersigned or as otherwise indicated below.

                                       Signature _____________________________


                                       Name for Registration _________________


                                       Mailing Address _______________________

                                       _______________________________________


                                       8


<PAGE>






                                           COMMON STOCK WARRANT NO. W-12/30/96-D

    THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "ACT"), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE
SOLD OR TRANSFERRED UNLESS SUCH SALE OR TRANSFER IS IN ACCORDANCE WITH THE
REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS OR SOME OTHER
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS IS
AVAILABLE WITH RESPECT THERETO.


                          ENSYS ENVIRONMENTAL PRODUCTS, INC.
                                 WARRANT TO PURCHASE
                                     COMMON STOCK


    1. Issuance.  This Warrant is issued to DSV Partners IV, L.P., by EnSys
Environmental Products, Inc., a Delaware corporation (referred to hereinafter,
with its successors, as the "Company"), on this 30th day of December, 1996 (the
"Warrant Issuance Date"), in consideration of the surrender to the Company for
cancellation of certain warrants to purchase common stock of Strategic
Diagnostics Inc., which warrants were issued on April 3, 1995.

    2. Purchase Price; Number of Shares. Subject to the terms and conditions
hereinafter set forth, the registered holder of this Warrant (the "Holder") is
entitled upon surrender of this Warrant with the subscription form annexed
hereto, duly executed, at the office of the Company, to purchase 11,169 shares
of common stock of the Company, par value $.01 per share (the "Common Stock"),
at the per share exercise price of $2.24 (the "Purchase Price").

    3. Payment of Purchase Price.  The Purchase Price may be paid (i) in cash
or by check, (ii) by the surrender by the Holder to the Company of any
promissory notes or other obligations issued by the Company, with all such notes
and obligations so surrendered being credited against the Purchase Price in an
amount equal to the principal amount thereof plus accrued interest to the date
of surrender, (iii) through delivery by the Holder to the Company of other
securities issued by the Company, with such securities being credited against
the Purchase Price in an amount equal to the fair market value thereof, as
determined in good faith by the Board of Directors of the Company (the "Board"),
or (iv) by any combination of the foregoing.  The Board shall promptly respond
in writing to an inquiry by the Holder as to the fair market value of any
securities the Holder may wish to deliver to the Company pursuant to clause
(iii) above.

    4. Net Issue Election.  The Holder may elect to receive, without the
payment by the Holder of any additional consideration, shares equal to the value
of this Warrant or any portion hereof by the surrender of this Warrant or such
portion to the Company, with the net issue election notice annexed hereto duly
executed, at the office of the Company; PROVIDED, that the Holder may not make
such an election unless (i) the Company has registered its securities pursuant
to the Securities Act of 1933, as amended, (the "Act") or in connection with
such registration or (ii) upon the expiration of this Warrant.  Thereupon, the
Company shall issue to




<PAGE>


the Holder such number of fully paid and nonassessable shares of Common Stock
as is computed using the following formula:

                                       X=Y(A-B)
                                         ------
                                          A

where X = the number of shares to be issued to the Holder pursuant to this
Section 4.

    Y = the number of shares covered by this Warrant in respect of which the
net issue election is made pursuant to this Section 4.

    A = the fair market value of one share of Common Stock.  If the Company's
securities are registered pursuant to the Act, the fair market value shall mean
the average high and low prices of the Common Stock on the day prior to the
exercise of this Warrant, if the Common Stock is being traded on a national
exchange; or the last reported sale price on the day prior to exercise of this
Warrant, if the Common Stock is traded on the Nasdaq National Market, and if the
Common Stock is not traded on a national exchange; or the closing bid price (or
average of bid prices) last quoted on the day prior to the exercise of this
Warrant by an established quotation service for over-the-counter securities, if
the Common Stock is not reported on the Nasdaq National Market or a national
exchange.  If the election occurs in connection with the registration of
securities, then the fair market value shall be the price offered to the
public.  Otherwise, the fair market value shall be as determined in good faith
by the Board, at the time the net issue election is made pursuant to this
Section 4.

    B = the Purchase Price in effect under this Warrant at the time the net
issue election is made pursuant to this Section 4.

The Board shall promptly respond in writing to an inquiry by the Holder as to
the fair market value of one share of Common Stock.

    5. Partial Exercise.  This Warrant may be exercised in part, and the Holder
shall be entitled to receive a new warrant, which shall be dated as of the date
of this Warrant, covering the number of shares in respect of which this Warrant
shall not have been exercised.

    6. Issuance Date.  The person or persons in whose name or names any
certificate representing shares of Common Stock is issued hereunder shall be
deemed to have become the holder of record of the shares represented thereby as
at the close of business on the date this Warrant is exercised with respect to
such shares, whether or not the transfer books of the Company shall be closed.

    7. Expiration Date.  This Warrant shall expire at the close of business on
April 3, 2000, and shall be void thereafter.

    8. Reserved Shares; Valid Issuance.  The Company covenants that it will at
all times


                                       2


<PAGE>


from and after the date hereof reserve and keep available such number of its
authorized shares of Common Stock, free from all preemptive or similar rights
therein, as will be sufficient to permit the exercise of this Warrant in full.
The Company further covenants that, assuming the receipt by the Company of the
consideration therefor, such shares as may be issued pursuant to the exercise
of this Warrant will, upon issuance, be duly and validly issued, fully paid and
nonassessable and free from all taxes, liens and charges with respect to the
issuance thereof.

    9. Dividends.  If at any time after the Warrant Issuance Date, the Company
subdivides the Common Stock, by split-up or otherwise, or combines the Common
Stock, or issues additional shares of Common Stock in payment of a stock
dividend on the Common Stock, the number of shares issuable on the exercise of
this Warrant shall forthwith be proportionately increased in the case of a
subdivision or stock dividend, or proportionately decreased in the case of a
combination, and the Purchase Price shall forthwith be proportionately decreased
in the case of a subdivision or stock dividend, or proportionately increased in
the case of a combination.  Whenever the Purchase Price is adjusted, as herein
provided, the Company shall promptly deliver to the Holder a certificate of an
officer of the Company setting forth the Purchase Price after such adjustment
and setting forth a brief statement on the facts requiring such adjustment.

    10. Mergers and Reclassifications.  If at any time after the Warrant
Issuance Date there shall be any reclassification, capital reorganization or
change of the Common Stock (other than as a result of a subdivision, combination
or stock dividend provided for in Section 9 hereof), or any consolidation of the
Company with, or merger of the Company into, another corporation or other
business organization (other than a consolidation or merger in which the Company
is the continuing corporation and which does not result in any reclassification
or change of the outstanding Common Stock), or any sale or conveyance to another
corporation or other business organization of all or substantially all of the
assets of the Company, then, as a condition of such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, lawful
provisions shall be made, and duly executed documents evidencing the same from
the Company or its successor shall be delivered to the Holder, so that the
Holder shall thereafter have the right to purchase, at a total price not to
exceed that payable upon the exercise of this Warrant in full, the kind and
amount of shares of stock and other securities and property receivable upon such
reclassification, reorganization, change, consolidation, merger, sale or
conveyance by a holder of the number of shares of Common Stock which might have
been purchased by the Holder immediately prior to such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, and in any
such case appropriate provisions shall be made with respect to the rights and
interest of the Holder to the end that the provisions hereof (including without
limitation, provisions for the adjustment of the Purchase Price and the number
of shares issuable hereunder) shall thereafter be applicable in relation to any
shares of stock or other securities and property thereafter deliverable upon
exercise hereof.

    11. Fractional Shares.  In no event shall any fractional share of Common
Stock be issued upon any exercise of this Warrant.

    12. Notices of Record Date, Etc.  In the event of:


                                       3


<PAGE>


         (a) any taking by the Company of a record of the holders of any class
of securities for the purpose of determining the holders thereof who are
entitled to receive any dividend or other distribution, or any right to
subscribe for, purchase or otherwise acquire any shares of stock of any class
or any other securities or property, or to receive any other right,

         (b) any reclassification of the capital stock of the Company, capital
reorganization of the Company, consolidation or merger involving the Company, or
sale or conveyance of all or substantially all of its assets, or

         (c) any voluntary or involuntary dissolution, liquidation or
winding-up of the Company,

then and in each such event the Company will mail or cause to be mailed to the
Holder a notice specifying (i) the date on which any such record is to be taken
for the purpose of such dividend, distribution or right, and stating the amount
and character of such dividend, distribution or right, or (ii) the date on which
any such reclassification, reorganization, consolidation, merger, sale or
conveyance, dissolution, liquidation or winding-up is to take place, and the
time, if any is to be fixed, as of which the holders of record in respect of
such event are to be determined.  Such notice shall be mailed at least 20 days
prior to the date specified in such notice on which any such action is to be
taken.

    13. Amendment.  The terms of this Warrant may be amended, modified or
waived only by written agreement of the Company and the Holder.

    14. Warrant Register Transfer, Etc.

              A. The Company will maintain a register containing the names and
addresses of the registered holders of outstanding Warrants.  The Holder may
change its address as shown on the warrant register by written notice to the
Company requesting such change.  Any notice or written communication required or
permitted to be given to the Holder may be given by certified mail or delivered
to the Holder at its address as shown on the warrant register.

              B. This Warrant may not be transferred or assigned in whole or in
part by the Holder without the prior written consent of the Company, which
consent shall not be unreasonably withheld (it being understood that the Company
may withhold consent to any transfer of the Warrant to any person seeking to
obtain control of the Company), except that prior written consent of the Company
will not be required for a transfer of the Warrant in whole by the Holder to an
"affiliate" of the Holder.  An "affiliate" of the Holder shall mean any other
person or entity directly or indirectly controlling, controlled by or under
direct or indirect common control with the Holder.  Prior to and as a condition
to effecting any such transfer the Holder shall deliver to the Company an
opinion of counsel reasonably satisfactory to the Company to the effect that
such transfer will comply with all applicable securities laws.


                                       4


<PAGE>


              C. In case this Warrant shall be mutilated, lost, stolen or
destroyed, the Company shall issue a new warrant of like tenor and denomination
and deliver the same (i) in exchange and substitution for and upon surrender and
cancellation of any mutilated Warrant, or (ii) in lieu of any Warrant lost,
stolen or destroyed, upon receipt of evidence reasonably satisfactory to the
Company of the loss, theft or destruction of such Warrant (including a
reasonably detailed affidavit with respect to the circumstances of any loss,
theft or destruction) and of indemnity reasonably satisfactory to the Company.

    15. No Impairment.  The Company will not, by amendment of its Certificate
of Incorporation or through any reclassification, capital reorganization,
consolidation, merger, sale or conveyance of assets, dissolution, liquidation,
issue or sale of securities or any other voluntary action, avoid or seek to
avoid the observance or performance of any of the terms of this Warrant, but
will at all times in good faith assist in the carrying out of all such terms and
in the taking of all such action as may be necessary or appropriate in order to
protect the rights of the Holder.

    16. Governing Law.  The provisions and terms of this Warrant shall be
governed by and construed in accordance with the internal laws of the State of
Delaware.

    17. Successors and Assigns.  This Warrant shall be binding upon the
Company's successors and assigns and shall inure to the benefit of the Holder's
successors, legal representatives and permitted assigns.

    18. Business Days.  If the last or appointed day for the taking of any
action required or the expiration of any right granted herein shall be a
Saturday or Sunday or a legal holiday in Delaware, then such action may be taken
or right may be exercised on the next succeeding day which is not a Saturday or
Sunday or such a legal holiday.


                                       5


<PAGE>


    IN WITNESS WHEREOF, the Company has caused this Warrant to be executed by
its duly authorized officer, under seal, as of the date above written.

                        ENSYS ENVIRONMENTAL PRODUCTS, INC.

                        By: /s/ Grover C. Wrenn                               
                            ----------------------------------------

                        Title: President and Chief Executive Officer
                               -------------------------------------


                                       6


<PAGE>


                                     SUBSCRIPTION


To:___________________________         Date:____________________________


    The undersigned hereby subscribes for _________________ shares of Common
Stock covered by this Warrant.  The certificate(s) for such shares shall be
issued in the name of the undersigned or as otherwise indicated below:

                                  Signature __________________________________


                                  Name for Registration ______________________


                                  Mailing Address ____________________________

                                  ____________________________________________


                                       7


<PAGE>


                              NET ISSUE ELECTION NOTICE


To:____________________________        Date:________________________

    The undersigned hereby elects under Section 4 to surrender the right to
purchase ___________ shares of Common Stock Pursuant to this Warrant.  The
certificate(s) for the shares issuable upon such net issue election shall be
issued in the name of the undersigned or as otherwise indicated below.

                                  Signature __________________________________


                                  Name for Registration ______________________


                                  Mailing Address ____________________________

                                  ____________________________________________


                                       8




<PAGE>



                                           COMMON STOCK WARRANT NO. W-12/30/96-E

    THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "ACT"), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE
SOLD OR TRANSFERRED UNLESS SUCH SALE OR TRANSFER IS IN ACCORDANCE WITH THE
REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS OR SOME OTHER
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS IS
AVAILABLE WITH RESPECT THERETO.


                          ENSYS ENVIRONMENTAL PRODUCTS, INC.
                                 WARRANT TO PURCHASE
                                     COMMON STOCK


         1. Issuance.  This Warrant is issued to DSV Partners IV, L.P., by
EnSys Environmental Products, Inc., a Delaware corporation (referred to
hereinafter, with its successors, as the "Company"), on this 30th day of
December, 1996 (the "Warrant Issuance Date"), in consideration of the surrender
to the Company for cancellation of certain warrants to purchase common stock of
Strategic Diagnostics Inc., which warrants were issued on April 18, 1995.

         2. Purchase Price; Number of Shares. Subject to the terms and
conditions hereinafter set forth, the registered holder of this Warrant (the
"Holder") is entitled upon surrender of this Warrant with the subscription form
annexed hereto, duly executed, at the office of the Company, to purchase 55,843
shares of common stock of the Company, par value $.01 per share (the "Common
Stock"), at the per share exercise price of $2.24 (the "Purchase Price").

         3. Payment of Purchase Price.  The Purchase Price may be paid (i) in
cash or by check, (ii) by the surrender by the Holder to the Company of any
promissory notes or other obligations issued by the Company, with all such notes
and obligations so surrendered being credited against the Purchase Price in an
amount equal to the principal amount thereof plus accrued interest to the date
of surrender, (iii) through delivery by the Holder to the Company of other
securities issued by the Company, with such securities being credited against
the Purchase Price in an amount equal to the fair market value thereof, as
determined in good faith by the Board of Directors of the Company (the "Board"),
or (iv) by any combination of the foregoing.  The Board shall promptly respond
in writing to an inquiry by the Holder as to the fair market value of any
securities the Holder may wish to deliver to the Company pursuant to clause
(iii) above.

         4. Net Issue Election.  The Holder may elect to receive, without the
payment by the Holder of any additional consideration, shares equal to the value
of this Warrant or any portion hereof by the surrender of this Warrant or such
portion to the Company, with the net issue election notice annexed hereto duly
executed, at the office of the Company; PROVIDED, that the Holder may not make
such an election unless (i) the Company has registered its securities pursuant
to the Securities Act of 1933, as amended, (the "Act") or in connection with
such




<PAGE>


registration or (ii) upon the expiration of this Warrant.  Thereupon, the
Company shall issue to the Holder such number of fully paid and nonassessable
shares of Common Stock as is computed using the following formula:

                                       X=Y(A-B)
                                         ------
                                          A

where X = the number of shares to be issued to the Holder pursuant to this
Section 4.

         Y = the number of shares covered by this Warrant in respect of which
the net issue election is made pursuant to this Section 4.

         A = the fair market value of one share of Common Stock.  If the
Company's securities are registered pursuant to the Act, the fair market value
shall mean the average high and low prices of the Common Stock on the day prior
to the exercise of this Warrant, if the Common Stock is being traded on a
national exchange; or the last reported sale price on the day prior to exercise
of this Warrant, if the Common Stock is traded on the Nasdaq National Market,
and if the Common Stock is not traded on a national exchange; or the closing bid
price (or average of bid prices) last quoted on the day prior to the exercise of
this Warrant by an established quotation service for over-the-counter
securities, if the Common Stock is not reported on the Nasdaq National Market or
a national exchange.  If the election occurs in connection with the registration
of securities, then the fair market value shall be the price offered to the
public.  Otherwise, the fair market value shall be as determined in good faith
by the Board, at the time the net issue election is made pursuant to this
Section 4.

         B = the Purchase Price in effect under this Warrant at the time the
net issue election is made pursuant to this Section 4.

The Board shall promptly respond in writing to an inquiry by the Holder as to
the fair market value of one share of Common Stock.

         5. Partial Exercise.  This Warrant may be exercised in part, and the
Holder shall be entitled to receive a new warrant, which shall be dated as of
the date of this Warrant, covering the number of shares in respect of which this
Warrant shall not have been exercised.

         6. Issuance Date.  The person or persons in whose name or names any
certificate representing shares of Common Stock is issued hereunder shall be
deemed to have become the holder of record of the shares represented thereby as
at the close of business on the date this Warrant is exercised with respect to
such shares, whether or not the transfer books of the Company shall be closed.

         7. Expiration Date.  This Warrant shall expire at the close of
business on April 18, 2000, and shall be void thereafter.


                                       2


<PAGE>


         8. Reserved Shares; Valid Issuance.  The Company covenants that it
will at all times from and after the date hereof reserve and keep available such
number of its authorized shares of Common Stock, free from all preemptive or
similar rights therein, as will be sufficient to permit the exercise of this
Warrant in full.  The Company further covenants that, assuming the receipt by
the Company of the consideration therefor, such shares as may be issued pursuant
to the exercise of this Warrant will, upon issuance, be duly and validly issued,
fully paid and nonassessable and free from all taxes, liens and charges with
respect to the issuance thereof.

         9. Dividends.  If at any time after the Warrant Issuance Date, the
Company subdivides the Common Stock, by split-up or otherwise, or combines the
Common Stock, or issues additional shares of Common Stock in payment of a stock
dividend on the Common Stock, the number of shares issuable on the exercise of
this Warrant shall forthwith be proportionately increased in the case of a
subdivision or stock dividend, or proportionately decreased in the case of a
combination, and the Purchase Price shall forthwith be proportionately decreased
in the case of a subdivision or stock dividend, or proportionately increased in
the case of a combination.  Whenever the Purchase Price is adjusted, as herein
provided, the Company shall promptly deliver to the Holder a certificate of an
officer of the Company setting forth the Purchase Price after such adjustment
and setting forth a brief statement on the facts requiring such adjustment.

         10. Mergers and Reclassifications.  If at any time after the Warrant
Issuance Date there shall be any reclassification, capital reorganization or
change of the Common Stock (other than as a result of a subdivision, combination
or stock dividend provided for in Section 9 hereof), or any consolidation of the
Company with, or merger of the Company into, another corporation or other
business organization (other than a consolidation or merger in which the Company
is the continuing corporation and which does not result in any reclassification
or change of the outstanding Common Stock), or any sale or conveyance to another
corporation or other business organization of all or substantially all of the
assets of the Company, then, as a condition of such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, lawful
provisions shall be made, and duly executed documents evidencing the same from
the Company or its successor shall be delivered to the Holder, so that the
Holder shall thereafter have the right to purchase, at a total price not to
exceed that payable upon the exercise of this Warrant in full, the kind and
amount of shares of stock and other securities and property receivable upon such
reclassification, reorganization, change, consolidation, merger, sale or
conveyance by a holder of the number of shares of Common Stock which might have
been purchased by the Holder immediately prior to such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, and in any
such case appropriate provisions shall be made with respect to the rights and
interest of the Holder to the end that the provisions hereof (including without
limitation, provisions for the adjustment of the Purchase Price and the number
of shares issuable hereunder) shall thereafter be applicable in relation to any
shares of stock or other securities and property thereafter deliverable upon
exercise hereof.

         11. Fractional Shares.  In no event shall any fractional share of
Common Stock be issued upon any exercise of this Warrant.


                                       3


<PAGE>


         12. Notices of Record Date, Etc.  In the event of:

              (a) any taking by the Company of a record of the holders of any
class of securities for the purpose of determining the holders thereof who are
entitled to receive any dividend or other distribution, or any right to
subscribe for, purchase or otherwise acquire any shares of stock of any class or
any other securities or property, or to receive any other right,

              (b) any reclassification of the capital stock of the Company,
capital reorganization of the Company, consolidation or merger involving the
Company, or sale or conveyance of all or substantially all of its assets, or

              (c) any voluntary or involuntary dissolution, liquidation or
winding-up of the Company,

then and in each such event the Company will mail or cause to be mailed to the
Holder a notice specifying (i) the date on which any such record is to be taken
for the purpose of such dividend, distribution or right, and stating the amount
and character of such dividend, distribution or right, or (ii) the date on which
any such reclassification, reorganization, consolidation, merger, sale or
conveyance, dissolution, liquidation or winding-up is to take place, and the
time, if any is to be fixed, as of which the holders of record in respect of
such event are to be determined.  Such notice shall be mailed at least 20 days
prior to the date specified in such notice on which any such action is to be
taken.

         13. Amendment.  The terms of this Warrant may be amended, modified or
waived only by written agreement of the Company and the Holder.

         14. Warrant Register Transfer, Etc.

                   A. The Company will maintain a register containing the names
and addresses of the registered holders of outstanding Warrants.  The Holder may
change its address as shown on the warrant register by written notice to the
Company requesting such change.  Any notice or written communication required or
permitted to be given to the Holder may be given by certified mail or delivered
to the Holder at its address as shown on the warrant register.

                   B. This Warrant may not be transferred or assigned in whole
or in part by the Holder without the prior written consent of the Company, which
consent shall not be unreasonably withheld (it being understood that the Company
may withhold consent to any transfer of the Warrant to any person seeking to
obtain control of the Company), except that prior written consent of the Company
will not be required for a transfer of the Warrant in whole by the Holder to an
"affiliate" of the Holder.  An "affiliate" of the Holder shall mean any other
person or entity directly or indirectly controlling, controlled by or under
direct or indirect common control with the Holder.  Prior to and as a condition
to effecting any such transfer the Holder shall deliver to the Company an
opinion of counsel reasonably satisfactory to the Company to the effect that
such transfer will comply with all applicable securities laws.


                                       4


<PAGE>


                   C. In case this Warrant shall be mutilated, lost, stolen or
destroyed, the Company shall issue a new warrant of like tenor and denomination
and deliver the same (i) in exchange and substitution for and upon surrender and
cancellation of any mutilated Warrant, or (ii) in lieu of any Warrant lost,
stolen or destroyed, upon receipt of evidence reasonably satisfactory to the
Company of the loss, theft or destruction of such Warrant (including a
reasonably detailed affidavit with respect to the circumstances of any loss,
theft or destruction) and of indemnity reasonably satisfactory to the Company.

         15. No Impairment.  The Company will not, by amendment of its
Certificate of Incorporation or through any reclassification, capital
reorganization, consolidation, merger, sale or conveyance of assets,
dissolution, liquidation, issue or sale of securities or any other voluntary
action, avoid or seek to avoid the observance or performance of any of the terms
of this Warrant, but will at all times in good faith assist in the carrying out
of all such terms and in the taking of all such action as may be necessary or
appropriate in order to protect the rights of the Holder.

         16. Governing Law.  The provisions and terms of this Warrant shall be
governed by and construed in accordance with the internal laws of the State of
Delaware.

         17. Successors and Assigns.  This Warrant shall be binding upon the
Company's successors and assigns and shall inure to the benefit of the Holder's
successors, legal representatives and permitted assigns.

         18. Business Days.  If the last or appointed day for the taking of any
action required or the expiration of any right granted herein shall be a
Saturday or Sunday or a legal holiday in Delaware, then such action may be taken
or right may be exercised on the next succeeding day which is not a Saturday or
Sunday or such a legal holiday.


                                       5


<PAGE>


         IN WITNESS WHEREOF, the Company has caused this Warrant to be executed
by its duly authorized officer, under seal, as of the date above written.

                             ENSYS ENVIRONMENTAL PRODUCTS, INC.

                             By: /s/ Grover C. Wrenn
                                 ----------------------------------------

                             Title: President and Chief Executive Officer
                                    -------------------------------------


                                       6


<PAGE>


                                     SUBSCRIPTION


To:___________________________         Date:____________________________


         The undersigned hereby subscribes for _________________ shares of
Common Stock covered by this Warrant.  The certificate(s) for such shares shall
be issued in the name of the undersigned or as otherwise indicated below:

                                       Signature _____________________________


                                       Name for Registration _________________


                                       Mailing Address _______________________

                                       _______________________________________


                                       7


<PAGE>


                              NET ISSUE ELECTION NOTICE


To:____________________________        Date:________________________

         The undersigned hereby elects under Section 4 to surrender the right
to purchase ___________ shares of Common Stock Pursuant to this Warrant.  The
certificate(s) for the shares issuable upon such net issue election shall be
issued in the name of the undersigned or as otherwise indicated below.

                                       Signature _____________________________


                                       Name for Registration _________________


                                       Mailing Address _______________________

                                       _______________________________________


                                       8




<PAGE>





                                           COMMON STOCK WARRANT NO. W-12/30/96-F

    THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "ACT"), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE
SOLD OR TRANSFERRED UNLESS SUCH SALE OR TRANSFER IS IN ACCORDANCE WITH THE
REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS OR SOME OTHER
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS IS
AVAILABLE WITH RESPECT THERETO.


                          ENSYS ENVIRONMENTAL PRODUCTS, INC.
                                 WARRANT TO PURCHASE
                                     COMMON STOCK


    1. Issuance.  This Warrant is issued to DSV Partners IV, L.P., by EnSys
Environmental Products, Inc., a Delaware corporation (referred to hereinafter,
with its successors, as the "Company"), on this 30th day of December, 1996 (the
"Warrant Issuance Date"), in consideration of the surrender to the Company for
cancellation of certain warrants to purchase common stock of Strategic
Diagnostics Inc., which warrants were issued on July 3, 1995.

    2. Purchase Price; Number of Shares. Subject to the terms and conditions
hereinafter set forth, the registered holder of this Warrant (the "Holder") is
entitled upon surrender of this Warrant with the subscription form annexed
hereto, duly executed, at the office of the Company, to purchase 27,922 shares
of common stock of the Company, par value $.01 per share (the "Common Stock"),
at the per share exercise price of $2.24 (the "Purchase Price").

    3. Payment of Purchase Price.  The Purchase Price may be paid (i) in cash
or by check, (ii) by the surrender by the Holder to the Company of any
promissory notes or other obligations issued by the Company, with all such notes
and obligations so surrendered being credited against the Purchase Price in an
amount equal to the principal amount thereof plus accrued interest to the date
of surrender, (iii) through delivery by the Holder to the Company of other
securities issued by the Company, with such securities being credited against
the Purchase Price in an amount equal to the fair market value thereof, as
determined in good faith by the Board of Directors of the Company (the "Board"),
or (iv) by any combination of the foregoing.  The Board shall promptly respond
in writing to an inquiry by the Holder as to the fair market value of any
securities the Holder may wish to deliver to the Company pursuant to clause
(iii) above.

    4. Net Issue Election.  The Holder may elect to receive, without the
payment by the Holder of any additional consideration, shares equal to the value
of this Warrant or any portion hereof by the surrender of this Warrant or such
portion to the Company, with the net issue election notice annexed hereto duly
executed, at the office of the Company; PROVIDED, that the Holder may not make
such an election unless (i) the Company has registered its securities pursuant
to the Securities Act of 1933, as amended, (the "Act") or in connection with
such registration or (ii) upon the expiration of this Warrant.  Thereupon, the
Company shall issue to




<PAGE>


the Holder such number of fully paid and nonassessable shares of Common Stock
as is computed using the following formula:

                                       X=Y(A-B)
                                         ------
                                          A

where X = the number of shares to be issued to the Holder pursuant to this
Section 4.

    Y = the number of shares covered by this Warrant in respect of which the
net issue election is made pursuant to this Section 4.

    A = the fair market value of one share of Common Stock.  If the Company's
securities are registered pursuant to the Act, the fair market value shall mean
the average high and low prices of the Common Stock on the day prior to the
exercise of this Warrant, if the Common Stock is being traded on a national
exchange; or the last reported sale price on the day prior to exercise of this
Warrant, if the Common Stock is traded on the Nasdaq National Market, and if the
Common Stock is not traded on a national exchange; or the closing bid price (or
average of bid prices) last quoted on the day prior to the exercise of this
Warrant by an established quotation service for over-the-counter securities, if
the Common Stock is not reported on the Nasdaq National Market or a national
exchange.  If the election occurs in connection with the registration of
securities, then the fair market value shall be the price offered to the public.
Otherwise, the fair market value shall be as determined in good faith by the
Board, at the time the net issue election is made pursuant to this Section 4.

    B = the Purchase Price in effect under this Warrant at the time the net
issue election is made pursuant to this Section 4.

The Board shall promptly respond in writing to an inquiry by the Holder as to
the fair market value of one share of Common Stock.

    5. Partial Exercise.  This Warrant may be exercised in part, and the Holder
shall be entitled to receive a new warrant, which shall be dated as of the date
of this Warrant, covering the number of shares in respect of which this Warrant
shall not have been exercised.

    6. Issuance Date.  The person or persons in whose name or names any
certificate representing shares of Common Stock is issued hereunder shall be
deemed to have become the holder of record of the shares represented thereby as
at the close of business on the date this Warrant is exercised with respect to
such shares, whether or not the transfer books of the Company shall be closed.

    7. Expiration Date.  This Warrant shall expire at the close of business on
July 3, 2000, and shall be void thereafter.

    8. Reserved Shares; Valid Issuance.  The Company covenants that it will at
all times


                                       2


<PAGE>


from and after the date hereof reserve and keep available such number of its
authorized shares of Common Stock, free from all preemptive or similar rights
therein, as will be sufficient to permit the exercise of this Warrant in full.
The Company further covenants that, assuming the receipt by the Company of the
consideration therefor, such shares as may be issued pursuant to the exercise
of this Warrant will, upon issuance, be duly and validly issued, fully paid
and nonassessable and free from all taxes, liens and charges with respect to
the issuance thereof.

    9. Dividends.  If at any time after the Warrant Issuance Date, the Company
subdivides the Common Stock, by split-up or otherwise, or combines the Common
Stock, or issues additional shares of Common Stock in payment of a stock
dividend on the Common Stock, the number of shares issuable on the exercise of
this Warrant shall forthwith be proportionately increased in the case of a
subdivision or stock dividend, or proportionately decreased in the case of a
combination, and the Purchase Price shall forthwith be proportionately decreased
in the case of a subdivision or stock dividend, or proportionately increased in
the case of a combination.  Whenever the Purchase Price is adjusted, as herein
provided, the Company shall promptly deliver to the Holder a certificate of an
officer of the Company setting forth the Purchase Price after such adjustment
and setting forth a brief statement on the facts requiring such adjustment.

    10. Mergers and Reclassifications.  If at any time after the Warrant
Issuance Date there shall be any reclassification, capital reorganization or
change of the Common Stock (other than as a result of a subdivision, combination
or stock dividend provided for in Section 9 hereof), or any consolidation of the
Company with, or merger of the Company into, another corporation or other
business organization (other than a consolidation or merger in which the Company
is the continuing corporation and which does not result in any reclassification
or change of the outstanding Common Stock), or any sale or conveyance to another
corporation or other business organization of all or substantially all of the
assets of the Company, then, as a condition of such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, lawful
provisions shall be made, and duly executed documents evidencing the same from
the Company or its successor shall be delivered to the Holder, so that the
Holder shall thereafter have the right to purchase, at a total price not to
exceed that payable upon the exercise of this Warrant in full, the kind and
amount of shares of stock and other securities and property receivable upon such
reclassification, reorganization, change, consolidation, merger, sale or
conveyance by a holder of the number of shares of Common Stock which might have
been purchased by the Holder immediately prior to such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, and in any
such case appropriate provisions shall be made with respect to the rights and
interest of the Holder to the end that the provisions hereof (including without
limitation, provisions for the adjustment of the Purchase Price and the number
of shares issuable hereunder) shall thereafter be applicable in relation to any
shares of stock or other securities and property thereafter deliverable upon
exercise hereof.

    11. Fractional Shares.  In no event shall any fractional share of Common
Stock be issued upon any exercise of this Warrant.

    12. Notices of Record Date, Etc.  In the event of:


                                       3


<PAGE>


         (a) any taking by the Company of a record of the holders of any class
of securities for the purpose of determining the holders thereof who are
entitled to receive any dividend or other distribution, or any right to
subscribe for, purchase or otherwise acquire any shares of stock of any class or
any other securities or property, or to receive any other right,

         (b) any reclassification of the capital stock of the Company, capital
reorganization of the Company, consolidation or merger involving the Company, or
sale or conveyance of all or substantially all of its assets, or

         (c) any voluntary or involuntary dissolution, liquidation or
winding-up of the Company,

then and in each such event the Company will mail or cause to be mailed to the
Holder a notice specifying (i) the date on which any such record is to be taken
for the purpose of such dividend, distribution or right, and stating the amount
and character of such dividend, distribution or right, or (ii) the date on which
any such reclassification, reorganization, consolidation, merger, sale or
conveyance, dissolution, liquidation or winding-up is to take place, and the
time, if any is to be fixed, as of which the holders of record in respect of
such event are to be determined.  Such notice shall be mailed at least 20 days
prior to the date specified in such notice on which any such action is to be
taken.

    13. Amendment.  The terms of this Warrant may be amended, modified or
waived only by written agreement of the Company and the Holder.

    14. Warrant Register Transfer, Etc.

              A. The Company will maintain a register containing the names and
addresses of the registered holders of outstanding Warrants.  The Holder may
change its address as shown on the warrant register by written notice to the
Company requesting such change.  Any notice or written communication required or
permitted to be given to the Holder may be given by certified mail or delivered
to the Holder at its address as shown on the warrant register.

              B. This Warrant may not be transferred or assigned in whole or in
part by the Holder without the prior written consent of the Company, which
consent shall not be unreasonably withheld (it being understood that the Company
may withhold consent to any transfer of the Warrant to any person seeking to
obtain control of the Company), except that prior written consent of the Company
will not be required for a transfer of the Warrant in whole by the Holder to an
"affiliate" of the Holder.  An "affiliate" of the Holder shall mean any other
person or entity directly or indirectly controlling, controlled by or under
direct or indirect common control with the Holder.  Prior to and as a condition
to effecting any such transfer the Holder shall deliver to the Company an
opinion of counsel reasonably satisfactory to the Company to the effect that
such transfer will comply with all applicable securities laws.


                                       4


<PAGE>


              C. In case this Warrant shall be mutilated, lost, stolen or
destroyed, the Company shall issue a new warrant of like tenor and denomination
and deliver the same (i) in exchange and substitution for and upon surrender and
cancellation of any mutilated Warrant, or (ii) in lieu of any Warrant lost,
stolen or destroyed, upon receipt of evidence reasonably satisfactory to the
Company of the loss, theft or destruction of such Warrant (including a
reasonably detailed affidavit with respect to the circumstances of any loss,
theft or destruction) and of indemnity reasonably satisfactory to the Company.

    15. No Impairment.  The Company will not, by amendment of its Certificate
of Incorporation or through any reclassification, capital reorganization,
consolidation, merger, sale or conveyance of assets, dissolution, liquidation,
issue or sale of securities or any other voluntary action, avoid or seek to
avoid the observance or performance of any of the terms of this Warrant, but
will at all times in good faith assist in the carrying out of all such terms and
in the taking of all such action as may be necessary or appropriate in order to
protect the rights of the Holder.

    16. Governing Law.  The provisions and terms of this Warrant shall be
governed by and construed in accordance with the internal laws of the State of
Delaware.

    17. Successors and Assigns.  This Warrant shall be binding upon the
Company's successors and assigns and shall inure to the benefit of the Holder's
successors, legal representatives and permitted assigns.

    18. Business Days.  If the last or appointed day for the taking of any
action required or the expiration of any right granted herein shall be a
Saturday or Sunday or a legal holiday in Delaware, then such action may be taken
or right may be exercised on the next succeeding day which is not a Saturday or
Sunday or such a legal holiday.


                                       5


<PAGE>


    IN WITNESS WHEREOF, the Company has caused this Warrant to be executed by
its duly authorized officer, under seal, as of the date above written.

                        ENSYS ENVIRONMENTAL PRODUCTS, INC.

                        By: /s/ Grover C. Wrenn                               
                            ----------------------------------------

                        Title: President and Chief Executive Officer
                               -------------------------------------


                                       6


<PAGE>


                                     SUBSCRIPTION


To:___________________________         Date:____________________________


    The undersigned hereby subscribes for _________________ shares of Common
Stock covered by this Warrant.  The certificate(s) for such shares shall be
issued in the name of the undersigned or as otherwise indicated below:

                                  Signature __________________________________


                                  Name for Registration ______________________


                                  Mailing Address ____________________________

                                  ____________________________________________


                                       7


<PAGE>


                              NET ISSUE ELECTION NOTICE


To:____________________________        Date:________________________

    The undersigned hereby elects under Section 4 to surrender the right to
purchase ___________ shares of Common Stock Pursuant to this Warrant.  The
certificate(s) for the shares issuable upon such net issue election shall be
issued in the name of the undersigned or as otherwise indicated below.

                                  Signature __________________________________


                                  Name for Registration ______________________


                                  Mailing Address ____________________________

                                  ____________________________________________


                                       8




<PAGE>



                                           COMMON STOCK WARRANT NO. W-12/30/96-G

    THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "ACT"), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE
SOLD OR TRANSFERRED UNLESS SUCH SALE OR TRANSFER IS IN ACCORDANCE WITH THE
REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS OR SOME OTHER
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS IS
AVAILABLE WITH RESPECT THERETO.


                          ENSYS ENVIRONMENTAL PRODUCTS, INC.
                                 WARRANT TO PURCHASE
                                     COMMON STOCK


         1. Issuance.  This Warrant is issued to DSV Partners IV, L.P., by
EnSys Environmental Products, Inc., a Delaware corporation (referred to
hereinafter, with its successors, as the "Company"), on this 30th day of
December, 1996 (the "Warrant Issuance Date"), in consideration of the surrender
to the Company for cancellation of certain warrants to purchase common stock of
Strategic Diagnostics Inc., which warrants were issued on August 1, 1995.

         2. Purchase Price; Number of Shares. Subject to the terms and
conditions hereinafter set forth, the registered holder of this Warrant (the
"Holder") is entitled upon surrender of this Warrant with the subscription form
annexed hereto, duly executed, at the office of the Company, to purchase 27,922
shares of common stock of the Company, par value $.01 per share (the "Common
Stock"), at the per share exercise price of $2.24 (the "Purchase Price").

         3. Payment of Purchase Price.  The Purchase Price may be paid (i) in
cash or by check, (ii) by the surrender by the Holder to the Company of any
promissory notes or other obligations issued by the Company, with all such notes
and obligations so surrendered being credited against the Purchase Price in an
amount equal to the principal amount thereof plus accrued interest to the date
of surrender, (iii) through delivery by the Holder to the Company of other
securities issued by the Company, with such securities being credited against
the Purchase Price in an amount equal to the fair market value thereof, as
determined in good faith by the Board of Directors of the Company (the "Board"),
or (iv) by any combination of the foregoing.  The Board shall promptly respond
in writing to an inquiry by the Holder as to the fair market value of any
securities the Holder may wish to deliver to the Company pursuant to clause
(iii) above.

         4. Net Issue Election.  The Holder may elect to receive, without the
payment by the Holder of any additional consideration, shares equal to the value
of this Warrant or any portion hereof by the surrender of this Warrant or such
portion to the Company, with the net issue election notice annexed hereto duly
executed, at the office of the Company; PROVIDED, that the Holder may not make
such an election unless (i) the Company has registered its securities pursuant
to the Securities Act of 1933, as amended, (the "Act") or in connection with
such




<PAGE>


registration or (ii) upon the expiration of this Warrant.  Thereupon, the
Company shall issue to the Holder such number of fully paid and nonassessable
shares of Common Stock as is computed using the following formula:

                                       X=Y(A-B)
                                         ------
                                          A

where X = the number of shares to be issued to the Holder pursuant to this
Section 4.

         Y = the number of shares covered by this Warrant in respect of which
the net issue election is made pursuant to this Section 4.

         A = the fair market value of one share of Common Stock.  If the
Company's securities are registered pursuant to the Act, the fair market value
shall mean the average high and low prices of the Common Stock on the day prior
to the exercise of this Warrant, if the Common Stock is being traded on a
national exchange; or the last reported sale price on the day prior to exercise
of this Warrant, if the Common Stock is traded on the Nasdaq National Market,
and if the Common Stock is not traded on a national exchange; or the closing bid
price (or average of bid prices) last quoted on the day prior to the exercise of
this Warrant by an established quotation service for over-the-counter
securities, if the Common Stock is not reported on the Nasdaq National Market or
a national exchange.  If the election occurs in connection with the registration
of securities, then the fair market value shall be the price offered to the
public.  Otherwise, the fair market value shall be as determined in good faith
by the Board, at the time the net issue election is made pursuant to this
Section 4.

         B = the Purchase Price in effect under this Warrant at the time the
net issue election is made pursuant to this Section 4.

The Board shall promptly respond in writing to an inquiry by the Holder as to
the fair market value of one share of Common Stock.

         5. Partial Exercise.  This Warrant may be exercised in part, and the
Holder shall be entitled to receive a new warrant, which shall be dated as of
the date of this Warrant, covering the number of shares in respect of which this
Warrant shall not have been exercised.

         6. Issuance Date.  The person or persons in whose name or names any
certificate representing shares of Common Stock is issued hereunder shall be
deemed to have become the holder of record of the shares represented thereby as
at the close of business on the date this Warrant is exercised with respect to
such shares, whether or not the transfer books of the Company shall be closed.

         7. Expiration Date.  This Warrant shall expire at the close of
business on August 1, 2000, and shall be void thereafter.


                                       2


<PAGE>


         8. Reserved Shares; Valid Issuance.  The Company covenants that it
will at all times from and after the date hereof reserve and keep available such
number of its authorized shares of Common Stock, free from all preemptive or
similar rights therein, as will be sufficient to permit the exercise of this
Warrant in full.  The Company further covenants that, assuming the receipt by
the Company of the consideration therefor, such shares as may be issued pursuant
to the exercise of this Warrant will, upon issuance, be duly and validly issued,
fully paid and nonassessable and free from all taxes, liens and charges with
respect to the issuance thereof.

         9. Dividends.  If at any time after the Warrant Issuance Date, the
Company subdivides the Common Stock, by split-up or otherwise, or combines the
Common Stock, or issues additional shares of Common Stock in payment of a stock
dividend on the Common Stock, the number of shares issuable on the exercise of
this Warrant shall forthwith be proportionately increased in the case of a
subdivision or stock dividend, or proportionately decreased in the case of a
combination, and the Purchase Price shall forthwith be proportionately decreased
in the case of a subdivision or stock dividend, or proportionately increased in
the case of a combination.  Whenever the Purchase Price is adjusted, as herein
provided, the Company shall promptly deliver to the Holder a certificate of an
officer of the Company setting forth the Purchase Price after such adjustment
and setting forth a brief statement on the facts requiring such adjustment.

         10. Mergers and Reclassifications.  If at any time after the Warrant
Issuance Date there shall be any reclassification, capital reorganization or
change of the Common Stock (other than as a result of a subdivision, combination
or stock dividend provided for in Section 9 hereof), or any consolidation of the
Company with, or merger of the Company into, another corporation or other
business organization (other than a consolidation or merger in which the Company
is the continuing corporation and which does not result in any reclassification
or change of the outstanding Common Stock), or any sale or conveyance to another
corporation or other business organization of all or substantially all of the
assets of the Company, then, as a condition of such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, lawful
provisions shall be made, and duly executed documents evidencing the same from
the Company or its successor shall be delivered to the Holder, so that the
Holder shall thereafter have the right to purchase, at a total price not to
exceed that payable upon the exercise of this Warrant in full, the kind and
amount of shares of stock and other securities and property receivable upon such
reclassification, reorganization, change, consolidation, merger, sale or
conveyance by a holder of the number of shares of Common Stock which might have
been purchased by the Holder immediately prior to such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, and in any
such case appropriate provisions shall be made with respect to the rights and
interest of the Holder to the end that the provisions hereof (including without
limitation, provisions for the adjustment of the Purchase Price and the number
of shares issuable hereunder) shall thereafter be applicable in relation to any
shares of stock or other securities and property thereafter deliverable upon
exercise hereof.

         11. Fractional Shares.  In no event shall any fractional share of
Common Stock be issued upon any exercise of this Warrant.


                                       3


<PAGE>


         12. Notices of Record Date, Etc.  In the event of:

              (a) any taking by the Company of a record of the holders of any
class of securities for the purpose of determining the holders thereof who are
entitled to receive any dividend or other distribution, or any right to
subscribe for, purchase or otherwise acquire any shares of stock of any class or
any other securities or property, or to receive any other right,

              (b) any reclassification of the capital stock of the Company,
capital reorganization of the Company, consolidation or merger involving the
Company, or sale or conveyance of all or substantially all of its assets, or

              (c) any voluntary or involuntary dissolution, liquidation or
winding-up of the Company,

then and in each such event the Company will mail or cause to be mailed to the
Holder a notice specifying (i) the date on which any such record is to be taken
for the purpose of such dividend, distribution or right, and stating the amount
and character of such dividend, distribution or right, or (ii) the date on which
any such reclassification, reorganization, consolidation, merger, sale or
conveyance, dissolution, liquidation or winding-up is to take place, and the
time, if any is to be fixed, as of which the holders of record in respect of
such event are to be determined.  Such notice shall be mailed at least 20 days
prior to the date specified in such notice on which any such action is to be
taken.

         13. Amendment.  The terms of this Warrant may be amended, modified or
waived only by written agreement of the Company and the Holder.

         14. Warrant Register Transfer, Etc.

                   A. The Company will maintain a register containing the names
and addresses of the registered holders of outstanding Warrants.  The Holder may
change its address as shown on the warrant register by written notice to the
Company requesting such change.  Any notice or written communication required or
permitted to be given to the Holder may be given by certified mail or delivered
to the Holder at its address as shown on the warrant register.

                   B. This Warrant may not be transferred or assigned in whole
or in part by the Holder without the prior written consent of the Company, which
consent shall not be unreasonably withheld (it being understood that the Company
may withhold consent to any transfer of the Warrant to any person seeking to
obtain control of the Company), except that prior written consent of the Company
will not be required for a transfer of the Warrant in whole by the Holder to an
"affiliate" of the Holder.  An "affiliate" of the Holder shall mean any other
person or entity directly or indirectly controlling, controlled by or under
direct or indirect common control with the Holder.  Prior to and as a condition
to effecting any such transfer the Holder shall deliver to the Company an
opinion of counsel reasonably satisfactory to the Company to the effect that
such transfer will comply with all applicable securities laws.


                                       4


<PAGE>


                   C. In case this Warrant shall be mutilated, lost, stolen or
destroyed, the Company shall issue a new warrant of like tenor and denomination
and deliver the same (i) in exchange and substitution for and upon surrender and
cancellation of any mutilated Warrant, or (ii) in lieu of any Warrant lost,
stolen or destroyed, upon receipt of evidence reasonably satisfactory to the
Company of the loss, theft or destruction of such Warrant (including a
reasonably detailed affidavit with respect to the circumstances of any loss,
theft or destruction) and of indemnity reasonably satisfactory to the Company.

         15. No Impairment.  The Company will not, by amendment of its
Certificate of Incorporation or through any reclassification, capital
reorganization, consolidation, merger, sale or conveyance of assets,
dissolution, liquidation, issue or sale of securities or any other voluntary
action, avoid or seek to avoid the observance or performance of any of the terms
of this Warrant, but will at all times in good faith assist in the carrying out
of all such terms and in the taking of all such action as may be necessary or
appropriate in order to protect the rights of the Holder.

         16. Governing Law.  The provisions and terms of this Warrant shall be
governed by and construed in accordance with the internal laws of the State of
Delaware.

         17. Successors and Assigns.  This Warrant shall be binding upon the
Company's successors and assigns and shall inure to the benefit of the Holder's
successors, legal representatives and permitted assigns.

         18. Business Days.  If the last or appointed day for the taking of any
action required or the expiration of any right granted herein shall be a
Saturday or Sunday or a legal holiday in Delaware, then such action may be taken
or right may be exercised on the next succeeding day which is not a Saturday or
Sunday or such a legal holiday.


                                       5


<PAGE>


         IN WITNESS WHEREOF, the Company has caused this Warrant to be executed
by its duly authorized officer, under seal, as of the date above written.

                             ENSYS ENVIRONMENTAL PRODUCTS, INC.

                             By: /s/ Grover C. Wrenn                            
                                 ----------------------------------------

                             Title: President and Chief Executive Officer
                                    -------------------------------------


                                       6


<PAGE>


                                     SUBSCRIPTION


To:___________________________         Date:____________________________


         The undersigned hereby subscribes for _________________ shares of
Common Stock covered by this Warrant.  The certificate(s) for such shares shall
be issued in the name of the undersigned or as otherwise indicated below:

                                       Signature _____________________________


                                       Name for Registration _________________


                                       Mailing Address _______________________

                                       _______________________________________


                                       7


<PAGE>


                              NET ISSUE ELECTION NOTICE


To:____________________________        Date:________________________

         The undersigned hereby elects under Section 4 to surrender the right
to purchase ___________ shares of Common Stock Pursuant to this Warrant.  The
certificate(s) for the shares issuable upon such net issue election shall be
issued in the name of the undersigned or as otherwise indicated below.

                                       Signature _____________________________


                                       Name for Registration _________________


                                       Mailing Address _______________________

                                       _______________________________________


                                       8





<PAGE>

                                                          EXHIBIT 4


                             FOURTH AMENDED AND RESTATED
                                           
                             CERTIFICATE OF INCORPORATION
                                           
                                          OF
                                           
                              STRATEGIC DIAGNOSTICS INC.
                                           

                                      ARTICLE I.

                                         NAME

         The name of the Corporation is Strategic Diagnostics Inc.

                                     ARTICLE II.

                                  REGISTERED OFFICE

         The address of the registered office of the Corporation in the State
of Delaware is Corporation Trust Center, 1209 Orange Street, in the City of
Wilmington, County of New Castle.  The name of the registered agent of the
Corporation at such address is The Corporation Trust Company.
         .

                                      ARTICLE III. 

                                       PURPOSES
                                           
         The nature of the business or purposes to be conducted or promoted by
the Corporation is to engage in any lawful act or activity for which
corporations may be organized under the General Corporation Law of Delaware.

                                     ARTICLE IV.

                                    CAPITAL STOCK

    The total number of shares of all classes of capital stock which the
Corporation shall have the authority to issue is 54,664,362 shares, divided into
classes as follows:

         2,164,362 shares shall be shares of Series A Convertible
         Preferred Stock, with a par value of $.01 per share (the "Series
         A Convertible Preferred Stock");



<PAGE>

         17,500,000 shares shall be shares of Preferred Stock, with a par
         value of $.01 per share (the "Blank Check Preferred Stock"); and

         35,000,000 shares shall be shares of Common Stock, with a par
         value of $.01 per share (the "Common Stock");

The following is a statement of the powers, preferences, rights, qualifications,
limitations and restrictions of the Series A Convertible Preferred Stock, the
Blank Check Preferred Stock and the Common Stock:

                   PART A. Series A Convertible Preferred Stock

         1.   Number of Shares.  The series of Preferred Stock designated and
known as "Series A Convertible Preferred Stock" shall consist of 2,164,362
shares.

         2.   Voting.  Except as otherwise may be provided in these terms of
the Series A Convertible Preferred Stock or by law, the Series A Convertible
Preferred Stock and all other classes and series of stock of the Corporation
otherwise entitled to vote shall vote together as a single class on all actions
to be taken by the stockholders of the Corporation.  Each share of Series A
Convertible Preferred Stock shall entitle the holder thereof to such number of
votes per share on each such action as shall equal the nearest whole number of
shares of Common Stock into which each share of Series A Convertible Preferred
Stock is then convertible.

         3.   Dividends.  The holders of the Series A Convertible Preferred
Stock shall be entitled to receive, out of funds legally available therefor,
when and if declared by the Board of Directors, any dividend on or with respect
to Common Stock (other than a dividend payable solely in shares of Common Stock)
in an amount equal to the product obtained by multiplying the dividend declared
or payable on each share of Common Stock times the nearest whole number of
shares of Common Stock  into which each share of Series A Convertible Preferred
Stock is then convertible.  

         4.   Liquidation.  Upon any liquidation, dissolution or winding up of
the Corporation (other than in connection with a reorganization of the
Corporation in which the rights and preferences of the Series A Convertible
Preferred Stock are not adversely affected), whether voluntary or involuntary, 
the holders of Series A Convertible Preferred Stock shall be entitled, before
any distribution or payment is made upon any stock ranking on liquidation junior
to the Series A Convertible Preferred Stock, to be paid an amount equal to
$2.9466849  per share of Series A Convertible Preferred Stock up to an aggregate
maximum of $6,377,693 (in the aggregate, the "Liquidation Preference") (such
amount payable with respect to one share of Series A Convertible Preferred Stock
sometimes shall be referred to as the "Liquidation Payment"); provided, however,
that the Liquidation Preference shall be automatically reduced in an aggregate
amount equal to any dividends paid to the holders of Series A Convertible
Preferred Stock and the Liquidation Payment shall be reduced on a per share
basis for such payment of dividends.  If upon such liquidation, dissolution or
winding up of the Corporation, whether

                                      2


<PAGE>

voluntary or involuntary, the assets to be distributed among the holders of
Series A Convertible Preferred Stock shall be insufficient to permit payment to
the holders of the Series A Convertible Preferred Stock of the full Liquidation
Preference, then the entire assets of the Corporation legally available for
distribution shall be distributed ratably among the holders of Series A
Convertible Preferred Stock.  Upon any such liquidation, dissolution or winding
up of the Corporation, after the holders of Series A Convertible Preferred
Stock shall have been paid the full Liquidation Preference, the remaining net
assets of the Corporation may be distributed to the holders of stock ranking
on liquidation junior to the Series A Convertible Preferred Stock. Written
notice of such liquidation, dissolution or winding up, stating a payment date,
the amount of the Liquidation Payment and the place where said Liquidation
Payment shall be payable, shall be given by mail, postage prepaid, or by telex
to non-U.S. residents, not less than 20 days prior to the payment date stated
therein, to the holders of record of Series A Convertible Preferred Stock,
such notice to be addressed to each such holder at its address as shown by the
records of the Corporation. 

         5.   Restrictions.  At any time when shares of Series A Convertible
Preferred Stock are outstanding, except where the vote or written consent of the
holders of a greater number of shares of the Corporation is required by law or
by the Certificate of Incorporation, and in addition to any other vote required
by law or the Certificate of Incorporation, without the approval of the holders
of at least two-thirds of the then outstanding shares of Series A Convertible
Preferred Stock, given in writing or by vote at a meeting, consenting or voting
(as the case may be) separately as a series, the Corporation will not:

              5A.  Create or authorize the creation of any additional class or
series of shares of stock unless the same ranks junior to the Series A
Convertible Preferred Stock as to the distribution of assets on the liquidation,
dissolution or winding up of the Corporation, or increase the authorized amount
of the Series A Convertible Preferred Stock or increase the authorized amount of
any additional class or series of shares of stock unless the same ranks junior
to the Series A Convertible Preferred Stock as to the distribution of assets on
the liquidation, dissolution or winding up of the Corporation, or create or
authorize any obligation or security convertible into shares of Series A
Convertible Preferred Stock or into shares of any other class or series of stock
unless the same ranks junior to the Series A Convertible Preferred Stock as to
the distribution of assets on the liquidation, dissolution or winding up of the
Corporation; or

              5B.  Redeem or otherwise acquire any shares of Series A
Convertible Preferred Stock, except as expressly authorized in paragraph 7
hereof or pursuant to a purchase offer made pro rata to all holders of the
shares of Series A Convertible Preferred Stock on the basis of the aggregate
number of outstanding shares of Series A Convertible Preferred Stock then held
by each such holder.

         6.   Conversions.  The holders of shares of Series A Convertible
Preferred Stock shall have the following conversion rights:

                                      3

<PAGE>

              6A.  Right to Convert.  Subject to the terms and conditions of
this paragraph 6, the holder of any share or shares of Series A Convertible
Preferred Stock shall have the right, at its option at any time, to convert any
such shares of Series A Convertible Preferred Stock (except that upon any
liquidation of the Corporation the right of conversion shall terminate at the
close of business on the business day fixed for payment of the Liquidation
Payment) into an equal number of fully paid and nonassessable shares of Common
Stock, subject to adjustment as provided in subparagraphs 6D and 6E.  Such
rights of conversion shall be exercised by the holder thereof by giving written
notice that the holder elects to convert a stated number of shares of Series A
Convertible Preferred Stock into Common Stock and by surrender of a certificate
or certificates for the shares so to be converted to the Corporation at its
principal office (or such other office or agency of the Corporation as the
Corporation may designate by notice in writing to the holders of the Series A
Convertible Preferred Stock) at any time during its usual business hours on the
date set forth in such notice, together with a statement of the name or names
(with address) in which the certificate or certificates for shares of Common
Stock shall be issued.

              6B.  Issuance of Certificates; Time Conversion Effected. 
Promptly after the receipt of the written notice referred to in subparagraph 6A
and surrender of the certificate or certificates for the share or shares of
Series A Convertible Preferred Stock to be converted, the Corporation shall
issue and deliver, or cause to be issued and delivered, to the holder,
registered in such name or names as such holder may direct, a certificate or
certificates for the number of whole shares of Common Stock issuable upon the
conversion of such share or shares of Series A Convertible Preferred Stock.  To
the extent permitted by law, such conversion shall be deemed to have been
effected as of the close of business on the date on which such written notice
shall have been received by the Corporation and the certificate or certificates
for such share or shares shall have been surrendered as aforesaid, and at such
time the rights of the holder of such share or shares of Series A Convertible
Preferred Stock shall cease, and the person or persons in whose name or names
any certificate or certificates for shares of Common Stock shall be issuable
upon such conversion shall be deemed to have become the holder or holders of
record of the shares represented thereby.

              6C.  Fractional Shares; Dividends; Partial Conversion.  No
fractional shares shall be issued upon conversion of Series A Convertible
Preferred Stock into Common Stock and no payment or adjustment shall be made
upon any conversion on account of any cash dividends on the Common Stock issued
upon such conversion.  At the time of each conversion, the Corporation shall pay
in cash an amount equal to all dividends accrued and unpaid on the shares of
Series A Convertible Preferred Stock surrendered for conversion to the date upon
which such conversion is deemed to take place as provided in subparagraph 6B. 
In case the number of shares of Series A Convertible Preferred Stock represented
by the certificate or certificates surrendered pursuant to subparagraph 6A
exceeds the number of shares converted, the Corporation shall, upon such
conversion, execute and deliver to the holder, at the expense of the
Corporation, a new certificate or certificates for the number of shares of
Series A Convertible Preferred Stock represented by the certificate or
certificates surrendered which are not to be converted.  If any fractional share
of Common Stock would, except for the provisions of the first sentence of this
subparagraph 6C, be delivered upon such conversion, the Corporation, in lieu of

                                      4

<PAGE>

delivering such fractional share, shall pay to the holder surrendering the
Series A Convertible Preferred Stock for conversion an amount in cash equal to
the current market price of such fractional share as determined in good faith by
the Board of Directors of the Corporation.

              6D.  Subdivision or Combination of Common Stock.  In case the
Corporation shall at any time subdivide (by any stock split, stock dividend or
otherwise) its outstanding shares of Common Stock into a greater number of
shares,  the number of shares of Common Stock issuable upon conversion of each
share of Series A Convertible Preferred Stock shall be increased in proportion
to such increase in outstanding shares, and, conversely, in case the outstanding
shares of Common Stock shall be combined into a smaller number of shares, the
number of shares of Common Stock issuable upon conversion of each share of
Series A Convertible Preferred Stock shall be decreased in proportion to such
decrease in outstanding shares.

              6E.  Reorganization or Reclassification.  If any capital
reorganization or reclassification of the capital stock of the Corporation shall
be effected in such a way that holders of Common Stock shall be entitled to
receive stock, securities or assets with respect to or in exchange for Common
Stock, then, as a condition of such reorganization or reclassification, lawful
and adequate provisions shall be made whereby each holder of a share or shares
of Series A Convertible Preferred Stock shall thereupon have the right to
receive, upon the basis and upon the terms and conditions specified herein and
in lieu of the shares of Common Stock immediately theretofore receivable upon
the conversion of such share or shares of Series A Convertible Preferred Stock,
such shares of stock, securities or assets as may be issued or payable with
respect to or in exchange for a number of outstanding shares of such Common
Stock equal to the number of shares of such Common Stock immediately theretofore
receivable upon such conversion had such reorganization or reclassification not
taken place, and in any such case appropriate provisions shall be made with
respect to the rights and interests of such holder to the end that the
provisions hereof shall thereafter be applicable, as nearly as may be, in
relation to any shares of stock, securities or assets thereafter deliverable
upon the exercise of such conversion rights.

              6F.  Certain Notices.  In case at any time:

                   (1)  the Corporation shall declare any dividend upon its
Common Stock payable in cash or stock or make any other distribution to the
holders of its Common Stock;

                   (2)  the Corporation shall offer for subscription pro rata
to the holders of its Common Stock any additional shares of stock of any class
or other rights;

                   (3)  there shall be any capital reorganization or
reclassification of the capital stock of the Corporation, or a consolidation or
merger of the Corporation with or into, or a sale of all or substantially all
its assets to, another entity or entities; or

                                      5

<PAGE>

                   (4)  there shall be a voluntary or involuntary dissolution,
liquidation or winding up of the Corporation;

then, in any one or more of said cases, the Corporation shall give, by first
class mail, postage prepaid, or by telex to non U.S. residents, addressed to
each holder of any shares of Series A Convertible Preferred Stock at the address
of such holder as shown on the books of the corporation, (a) at least 20 days'
prior written notice of the date on which the books of the Corporation shall
close or a record shall be taken for such dividend, distribution or subscription
rights or for determining rights to vote in respect of any such reorganization,
reclassification, consolidation, merger, sale, dissolution, liquidation or
winding up and (b) in the case of any such reorganization, reclassification,
consolidation, merger, sale, dissolution, liquidation or winding up, at least 20
days' prior written notice of the date when the same shall take place.  Such
notice in accordance with the foregoing clause (a) shall also specify, in the
case of any such dividend, distribution or subscription rights, the date on
which the holders of Common Stock shall be entitled thereto and such notice in
accordance with the foregoing clause (b) shall also specify the date on which
the holders of Common Stock shall be entitled to exchange their Common Stock for
securities or other property deliverable upon such reorganization,
reclassification, consolidation, merger, sale, dissolution, liquidation or
winding up, as the case may be.

                   6G.  Stock to be Reserved.  The Corporation will at all
times reserve and keep available out of its authorized Common Stock, solely for
the purpose of issuance upon the conversion of Series A Convertible Preferred
Stock as herein provided, such number of shares of Common Stock as shall then be
issuable upon the conversion of all outstanding shares of Series A Convertible
Preferred Stock.  The Corporation covenants that, assuming the receipt by the
Corporation of the consideration therefor, all shares of Common Stock which
shall be so issued shall be duly and validly issued and fully paid and
nonassessable.

                   6H.  No Reissuance of Series A Convertible Preferred Stock. 
Shares of Series A Convertible Preferred Stock which are converted into shares
of Common Stock as provided herein shall be canceled and shall not be reissued.

                   6I.  Closing of Books.  The Corporation will at no time
close its transfer books against the transfer of any Series A Convertible
Preferred Stock or of any shares of Common Stock issued or issuable upon the
conversion of any shares of Series A Convertible Preferred Stock in any manner
which interferes with the timely conversion of such Series A Convertible
Preferred Stock, except as may otherwise be required to comply with applicable
securities laws.

                   6J.  Mandatory Conversion.  If the closing share price of
Common Stock listed on the NASDAQ National Market System equals or exceeds $4.50
per share for a period of forty-five (45) consecutive business days, all
outstanding shares of Series A Convertible Preferred Stock shall automatically
convert to shares of Common Stock.

                                      6

<PAGE>

                   7.   Redemption.  The shares of Series A Convertible
Preferred Stock shall be redeemed as follows:

                        7A.  Redemption at Holders' Option.  In the event the
Corporation enters into a merger, consolidation, recapitalization,
reorganization or any other transaction pursuant to which the Series A
Convertible Preferred Stock would be converted into or exchanged for: (i)
preferred stock with lesser rights or a lesser Liquidation Preference; or (ii)
for common stock that in the aggregate has a lesser aggregate fair market value
than the Liquidation Preference; or (iii) for an aggregate amount of cash that
is less than the Liquidation Preference; then on the written request (the
"Holder Redemption Request") of the holders of at least 66 2/3% of the
outstanding shares of Series A Convertible Preferred Stock, then at or before
the closing of such transaction, the Corporation shall redeem from each holder
of shares of Series A Convertible Preferred Stock all of the shares of Series A
Convertible Preferred Stock held by such holder for an aggregate amount equal to
the Liquidation Preference.

                        7B.  Redemption at Corporation's Option.  Upon at least
sixty (60) days' prior written notice, the Corporation may redeem effective at
any time on or after June 23, 2001, from each holder of shares of Series A
Convertible Preferred Stock all of the shares of Series A Convertible Preferred
Stock held by such holder.

                        7C.  Redemption Price and Payment.  The Series A
Convertible Preferred Stock to be redeemed pursuant to Subparagraph 7B shall be
redeemed by paying for each share in cash an amount equal to the Liquidation
Payment, such amount also being referred to as the "Redemption Price".  Such
payment shall be made in full to the holders entitled thereto.

                        7D.  Redemption Mechanics.  At least 20 but not more
than 30 days prior to the date of any redemption (the "Redemption Date"),
written notice (the "Redemption Notice") shall be given by the Corporation by
mail, postage prepaid, or by telex to non-U.S. residents for which telex
instructions shall have been provided to the Corporation for such purpose, to
each holder of record (at the close of business on the business day next
preceding the day on which the Redemption Notice is given) of shares of Series A
Convertible Preferred Stock notifying such holder of the redemption and
specifying the Redemption Price, the Redemption Date and the place where said
Redemption Price shall be payable.  The holders of at least 66-2/3% of the
Series A Convertible Preferred Stock may rescind any Holder Redemption Request
at any time prior to the close of business on the 10th day after receipt of the
Redemption Notice by giving written notice of rescission to the Corporation;
provided, that the holders of Series A Convertible Preferred Stock may not
thereafter submit a subsequent Holder Redemption Request in respect of the same
transaction.  The Redemption Notice shall be addressed to each holder at his
address as shown by the records of the Corporation.  From and after the close of
business on the Redemption Date, unless there shall have been a default in the
payment of the Redemption Price, all rights of holders of shares of Series A
Convertible Preferred Stock (except the right to receive the Redemption Price)
shall cease with respect to such shares, and such shares shall not thereafter be
transferred on the books of the Corporation or be deemed to be outstanding for
any purpose whatsoever.  If the funds of the Corporation legally available for
redemption of shares of

                                      7

<PAGE>

Series A Convertible Preferred Stock on the Redemption Date are insufficient to
redeem the total number of outstanding shares of Series A Convertible Preferred
Stock, the holders of shares of Series A Convertible Preferred Stock shall
share ratably in any funds legally available for redemption of such shares
according to the respective amounts which would be payable with respect to the
full number of shares owned by them if all such outstanding shares were
redeemed in full.  The shares of Series A Convertible Preferred Stock not
redeemed shall remain outstanding and entitled to all rights and preferences
provided herein.  At any time thereafter when additional funds of the
Corporation are legally available for the redemption of such shares of Series A
Convertible Preferred Stock, such funds will be used, at the end of the next
succeeding fiscal quarter, to redeem the balance of such shares, or such
portion thereof for which funds are then legally available, on the basis set
forth above.

                        7E.  Redeemed or Otherwise Acquired Shares to be
Retired.  Any shares of Series A Convertible Preferred Stock redeemed pursuant
to this paragraph 7 or otherwise acquired by the Corporation in any manner
whatsoever shall be canceled and shall not under any circumstances be reissued;
and the Corporation may from time to time take such appropriate corporate action
as may be necessary to reduce accordingly the number of authorized shares of
Series A Convertible Preferred Stock.

                         PART B.  Blank Check Preferred Stock

         1.   Designation and Amount.  The designation of this class of capital
stock shall be "Blank Check Preferred Stock," par value $.01 per share.  Subject
to the provisions of this Article IV and the express provisions of each series
of Blank Check Preferred Stock, the Board of Directors is hereby empowered to
cause the Corporation to issue from time to time, in one or more series, up to
17,500,000 shares of Blank Check Preferred Stock.

         2.   Rights.  The powers, designations, preferences, terms,
conditions, privileges and other rights of each series of Blank Check Preferred
Stock shall be determined by the Board of Directors in accordance with Section
151 of the Delaware General Corporation Law, subject to the provisions of Part
A, Paragraph 5A of this Article IV.  Except in respect of the particulars fixed
by the Board of Directors for each such series, all Blank Check Preferred Stock
shall be of equal rank and identical.

                               PART C.  Common Stock

         1.   Designation and Amount.  The designation of this class of capital
stock shall be "Common Stock," par value $.01 per share ("Common Stock").  The
number of authorized shares of Common Stock may be increased or decreased (but
not below the number of shares thereof then outstanding) by the affirmative vote
of the holders of the majority of the stock of the Corporation entitled to vote,
irrespective of the provisions of Section 242(b)(2) of the Delaware General
Corporation Law.

                                      8

<PAGE>

         2.   Voting. Each share of Common Stock shall have one vote upon all
matters to be voted on by the holders of Common Stock, which voting rights shall
not be cumulative.

         3.   Other Rights. Each share of Common Stock shall be entitled to
participate equally in all dividends payable with respect to the Common Stock
and to share ratably, subject to the rights and preferences of the Series A
Convertible Preferred Stock and/or any series of the Blank Check Preferred
Stock, in all assets of the Corporation in the event of any voluntary or
involuntary liquidation, dissolution or winding up of the affairs of the
Corporation, or upon any distribution of the assets of the Corporation.

                                      ARTICLE V.
                            CERTAIN BUSINESS COMBINATIONS

              PART A. Vote Required for Certain Business Combinations.

         1.   Required Vote for Certain Business Combinations.  In addition to
any affirmative vote required by law or by this Certificate of Incorporation,
and except as otherwise expressly provided in Paragraph 2 of this Article V,
Part A:

              1A.  any merger or consolidation of the Corporation or any
Subsidiary (as hereinafter defined) with (a) any Interested Stockholder (as
hereinafter defined) or (b) any other corporation or entity (whether or not
itself an Interested Stockholder) which is, or after such merger or
consolidation would be, an Affiliate (as hereinafter defined) of any Interested
Stockholder; or

              1B.  any sale, lease, exchange, mortgage, pledge, transfer or
other disposition (in one transaction or a series of transactions) to or with
any Interested Stockholder or any Affiliate of any Interested Stockholder of any
assets of the Corporation or any Subsidiary having an aggregate Fair Market
Value (as hereinafter defined) of $5,000,000 or more; or

              1C.  the issuance or transfer by the Corporation or any
Subsidiary (in one transaction or a series of transactions) of any securities of
the Corporation or any Subsidiary to any Interested Stockholder or any Affiliate
of any Interested Stockholder in exchange for cash, securities or other property
(or a combination thereof) having an aggregate Fair Market Value of $5,000,000
or more; or

              1D.  the adoption of any plan or proposal for the liquidation,
dissolution or winding up of the Corporation proposed by or on behalf of any
Interested Stockholder or any Affiliate of any Interested Stockholder; or

              1E.  any reclassification of securities (including any reverse
stock split), or recapitalization of the Corporation, or any merger or
consolidation of the Corporation with any of its Subsidiaries or any other
transaction (whether or not with or into or otherwise involving any Interested
Stockholder) which has the effect, directly or indirectly, of increasing the

                                      9

<PAGE>

proportionate share of the outstanding shares of any class of equity or
convertible securities of the Corporation or any Subsidiary which is directly or
indirectly owned by any Interested Stockholder or any Affiliate of any
Interested Stockholder;

shall require, subject to Paragraph 2 of this Article V, Part A, the affirmative
vote of the holders of at least two-thirds of the voting power of the then
outstanding Voting Stock (as hereinafter defined), voting together as a single
class at a duly constituted meeting of stockholders called expressly for such
purpose.  Such affirmative vote shall be required notwithstanding the fact that
no vote may be required, or that a lesser percentage may be specified, by law.

         2.   Definition of "Business Combination.  The term "Business
Combination" as used in this Article V shall mean any transaction which is
referred to in any one or more of Subparagraphs (1A) through (1E) of this
Paragraph 1 of Article V, Part A.

                        PART B.  When Higher Vote is Not Required.

    The provisions of Paragraph 1 of this Article V, Part A, shall not be
applicable to any particular Business Combination, and such Business Combination
shall require only such affirmative vote, if any, as is required by law and any
other provision of this Certificate of Incorporation, if all of the conditions
specified in either of the following Paragraph 1 or 2 or this Part B are met:

         1.   Approval by Continuing Directors.  The Business Combination shall
have been approved by the affirmative vote of a majority of the Continuing
Directors (as herein defined) then in office.

         2.   Price and Procedure Requirements.  All of the following
conditions shall have been met:

              2A.  The aggregate amount of the cash and the Fair Market Value,
as of the date of the consummation of the Business Combination, of consideration
other than cash to be received per share by holders of common stock in such
Business Combination shall be at least equal to the highest of the following:

                   (1)  (if applicable) the highest per share price (including
any brokerage commissions, transfer taxes and soliciting dealers' fees) paid by
the Interested Stockholder for any shares of common stock acquired by it (1)
within the two-year period immediately prior to and including the first public
announcement of the proposal of the Business Combination (the "Announcement
Date") or (2) in the transaction in which it became an Interested Stockholder,
whichever is higher; and

                   (2)  the Fair Market Value per share of common stock on the
Announcement Date or on the date on which the Interested Stockholder became an
Interested

                                     10

<PAGE>

Stockholder (such latter date is referred to in this Article V as the
"Determination Date"), whichever is higher.

              2B.  The aggregate amount of the cash and the Fair Market Value,
as of the date of the date of the consummation of the Business Combination, of
consideration other than cash to be received per share by holders of shares of
any other class of outstanding Voting Stock in such Business Combination shall
be at least equal to the highest of the following (it being intended that the
requirements of this Subparagraph 2B shall be required to be met with respect to
every other class of outstanding Voting Stock, whether or not the Interested
Stockholder has previously acquired any shares of a particular class of Voting
Stock):

                   (1)  (if applicable) the highest per share price (including
any brokerage commissions, transfer taxes and soliciting dealers' fees) paid by
the Interested Stockholder for any shares of such class of Voting Stock acquired
by it (1) within the two-year period immediately prior to and including the
Announcement Date or (2) in the transaction in which it became an Interested
Stockholder, whichever is higher;

                   (2)  (if applicable) the highest preferential amount per
share which the holders of shares of such class of Voting Stock are entitled to
receive from the Corporation in the event of any voluntary or involuntary
liquidation, dissolution or winding up of the Corporation; and

                   (3)  the Fair Market Value per share of such class of voting
Stock on the Announcement Date or on the Determination Date, whichever is
higher.

              2C.  The consideration to be received by holders of a particular
class of outstanding Voting Stock shall be in cash or in the same form as the
Interested Stockholder has previously paid for shares of such class of Voting
Stock.  If the Interested Stockholder has paid for shares of any class of Voting
Stock with varying forms of consideration, the form of consideration for such
class of Voting Stock shall be either cash or the form used to acquire the
largest number of shares of such class of Voting Stock previously acquired by
such Interested Stockholder.

              2D.  After such Interested Stockholder has become an Interested
Stockholder and prior to the consummation of such Business Combination: (a)
there shall have been (1) no failure to declare and pay at regular dates
therefor the full amount of any dividends (whether or not cumulative) payable on
any class or series of preferred stock, except as approved by the affirmative
vote of a majority of the Continuing Directors; (2) no reduction in the annual
rate of dividends paid on the common stock (except as necessary to reflect any
subdivision of the common stock), except as approved by the affirmative vote of
a majority of the Continuing Directors; and (3) an increase in such annual rate
of dividends as necessary to reflect any reclassification (including any reverse
stock split), recapitalization, reorganization or any similar transaction which
has the effect of reducing the number of outstanding shares of the common stock,
unless the failure so to increase such annual rate is approved by the
affirmative vote of a

                                     11

<PAGE>

majority of the Continuing Directors; and (b) such Interested Stockholder shall
not have become the beneficial owner of any additional shares of Voting Stock
except as part of the transaction which results in such Interested Stockholder
becoming an Interested Stockholder.

              2E.  After such Interested Stockholder has become an Interested
Stockholder, such Interested Stockholder shall not have received the benefit,
directly or indirectly (except proportionately as a stockholder), of any loans,
advances, guarantees, pledges or other financial assistance or any tax credits
or other tax advantages provided by the Corporation, whether in anticipation of
or in connection with such Business Combination or otherwise, unless such
transaction shall have been approved or ratified by the affirmative vote of a
majority of the Continuing Directors after such person shall have become an
Interested Stockholder.

              2F.  A proxy or information statement describing the proposed
Business Combination and complying with the requirements of the Securities
Exchange Act of 1934 and the rules and regulations thereunder (or any subsequent
provisions replacing such Act, rules and regulations) shall be mailed to public
stockholders of the Corporation at least 20 days prior to the consummation of
such Business Combination (whether or not such proxy or information statement is
required to be mailed pursuant to such Act, rules or regulations or subsequent
provisions thereof).

                              PART C.  Certain Definitions.

    For the purposes of this Article V:

         1.   A "person" shall mean an individual, a Group Acting in Concert, a
corporation, a partnership, an association, a joint stock company, a trust, a
business trust, a government or political subdivision, any unincorporated
organization, or any other association or entity.

         2.   "Interested Stockholder" shall mean any person who or which:

              2A.  is the beneficial owner, directly or indirectly, of 15% or
more of the voting power of the then outstanding shares of Voting Stock; or

              2B.  is an Affiliate of the Corporation and at any time within
the two-year period immediately prior to and including the date in question was
the beneficial owner, directly or indirectly, of 15% or more of the voting power
of the then outstanding shares of Voting Stock; or

              2C.  is an assignee of or has otherwise succeeded to the
beneficial ownership of any shares of Voting Stock which were at any time within
the two-year period immediately prior to and including the date in question
beneficially owned by any Interested Stockholder, if such assignment or
succession shall have occurred in the course of a transaction or series of
transactions not involving a public offering within the meaning of the
Securities Act

                                     12

<PAGE>

of 1933 (or any subsequent provisions replacing such Act or the rules and
regulations promulgated thereunder) and such assignment or succession was not
approved by a majority of the Continuing Directors;

provided, however, that the term "Interested Stockholder" shall not include (a)
the Corporation; (b) any Subsidiary of the Corporation; (c) any person, directly
or indirectly, owning of record or beneficially 100% of the issued and
outstanding capital stock of the Corporation (other than directors' qualifying
shares, if any); (d) any employee benefit plan or compensation arrangement of
the Corporation or any Subsidiary of the Corporation; (e) any person holding
shares of voting Stock organized, appointed or established by the Corporation or
any Subsidiary for or pursuant to the terms of any such employee benefit plan or
compensation arrangement; or (f) any Grandfathered Person unless such
Grandfathered Person becomes, after the closing of the initial public offering
of shares of common stock of the Corporation, the beneficial owner of more than
the Grandfathered Percentage of the Voting Stock then outstanding.  Any
Grandfathered Person who becomes, after the close of business on the date of the
closing of the initial public offering of shares of common stock of the
Corporation, the beneficial owner of less than 15% of the voting power of the
then outstanding shares of Voting Stock shall cease to be a Grandfathered
Person.

Notwithstanding the foregoing, no person shall become an "Interested
Stockholder" as the result of an acquisition of Voting Stock by the Corporation
which, by reducing the number of shares outstanding, increases the proportionate
number of shares beneficially owned by such person to 15% (or, if applicable,
the Grandfathered Percentage with respect to such person) or more of the voting
power of the then outstanding shares of Voting Stock; provided, however, that if
a person shall become the beneficial owner of 15% (or, if applicable, the
Grandfathered Percentage with respect to such person) or more of the voting
power of the then outstanding shares of Voting Stock by reason of share
purchases by the Corporation and shall, after such share purchases by the
Corporation, become the beneficial owner of any additional shares of Voting
Stock of the Corporation (other than any shares of Voting Stock issued to such
person as a result of a stock dividend, stock split, reclassification,
recapitalization, or other similar transaction involving the issuance of shares
of Voting Stock on a pro rata basis to all holders of voting Stock), then such
person shall be deemed to be an "Interested Stockholder" if immediately
thereafter the voting power of the shares of Voting Stock beneficially owned by
such person equals or exceeds 15% (or in the case of a Grandfathered Person, the
Grandfathered Percentage with respect to such person) or more of the voting
power of all of the shares of Voting Stock then outstanding.

         3.   A person shall be deemed the "beneficial owner" of, and shall be
deemed to beneficially own, any Voting Stock:

              3A.  which such person or any of such person's Affiliates or
Associates, directly or indirectly, beneficially owns (as determined pursuant to
Rule 13d-3 of the Rules and Regulations promulgated by the Securities and
Exchange Commission under the Securities Exchange Act of 1934, as amended (the
"1934 Act")); or

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<PAGE>

              3B.  which such person or any of its Affiliates or Associates,
directly or indirectly, has or shares with respect to the Voting Stock (a) the
right to acquire, or direct the acquisition of (whether such right is
exercisable immediately, or only after the passage of time or upon the
satisfaction of any conditions, or both), such Voting Stock pursuant to any
agreement, arrangement, understanding or otherwise (whether or not in writing)
(other than customary arrangements with and between underwriters and selling
group members with respect to a bona fide public offering of securities) or upon
the exercise of conversion rights, exchange rights, warrants or options, or
otherwise; provided, however, that a person shall not be deemed the "beneficial
owner" of, or to "beneficially own," securities tendered pursuant to a tender or
exchange offer made by or on behalf of such person or any of such person's
Affiliates or Associates until such tendered securities are accepted for
purchase or exchange, (b) the right to vote, or to direct the voting of, such
Voting Stock pursuant to any agreement, arrangement, understanding or otherwise
(whether or not in writing) (provided that a person shall not be deemed to be
the beneficial owner of any securities if the agreement, arrangement or
understanding to vote such security arises solely from a revocable proxy given
in response to a public proxy or consent solicitation made pursuant to, and in
accordance with, the Rules and Regulations promulgated under the 1934 Act and is
not also then reportable by such person on Schedule 13D under the 1934 Act (or
any comparable or successor report)), or (c) the right to dispose of, or to
direct the disposition of, such Voting Stock pursuant to any agreement,
arrangement, understanding or otherwise (whether or not in writing) (other than
customary arrangement with and between underwriters and selling group members
with respect to a bona fide public offering of securities ); or

              3C.  which is beneficially owned, directly or indirectly, by any
other person (or any Affiliate or Associate thereof) with which such person or
any of such person's Affiliates or Associates has any agreement, arrangement,
understanding or otherwise (whether or not in writing) (other than customary
arrangements with and between underwriters and selling group members with
respect to a bona fide public offering of securities) for the purpose of
acquiring, holding, voting (except pursuant to a revocable proxy described in
Subparagraph 3B above) or disposing of any shares of Voting Stock.

provided, however, that (1) no person engaged in business as an underwriter of
securities shall be deemed the beneficial owner of any securities acquired
through such person's participation as an underwriter in good faith in a firm
commitment underwriting until the expiration of 40 days after the date of such
acquisition and (2) no person who is a director or an officer of the Corporation
shall be deemed, solely as a result of his or her participation as director or
officer of the Corporation, the beneficial owner of any securities of the
Corporation that are beneficially owned by any other director or officer of the
Corporation.

              3D.  Notwithstanding anything in the definition of beneficial
owner to the contrary, the phrase "then outstanding," when used with reference
to a person's beneficial ownership of securities of the Corporation, shall mean
the number of such securities then issued and outstanding together with the
number of such securities not then actually issued and outstanding which such
person would be deemed to own beneficially hereunder.

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<PAGE>

              3E.  "Affiliate" and "Associate" shall have the respective
meanings ascribed to such terms in Rule 12b-2 f the General Rules and
Regulations under the 1934 Act (or any subsequent provisions replacing the 1934
Act or the rules and regulations promulgated thereunder); provided, however,
that no person who is a director or officer of the Corporation shall be deemed
an Affiliate or Associate of any other director or officer of the Corporation
solely as a result of his or her position as a director or officer of the
Corporation.

              3F.  "Subsidiary" means any corporation of which a majority of
any class of equity security is owned, directly or indirectly, by the
Corporation; provided, however, that for the purposes of the definition of
Interested Stockholder set forth in Paragraph 2 of this Part C, the term
"Subsidiary" shall mean only a corporation of which a majority of each class of
equity security is owned, directly or indirectly, by the Corporation.

              3G.  "Continuing Director" means (i) any member of the Board of
Directors of the Corporation who is not an Interested Stockholder of an
Affiliate or Associate of an Interested Stockholder and was a member of the
Board of Directors prior to the time that the interested Stockholder became an
Interested Stockholder, and (ii) any person who subsequently becomes a member of
the Corporation's Board of Directors who is not an Associate or Affiliate of an
Interested Stockholder and is recommended or approved by the affirmative vote of
a majority of the Continuing Directors.

              3H.  "Fair Market Value" means:

                   (1)  in the case of stock, the highest closing sale price
during the 30-day period immediately prior to and including the date in question
of a share of such stock on the principal United States securities exchange
registered under the 1934 Act (or any subsequent provisions replacing such Act
or rules or regulations promulgated thereunder) on which such stock is listed,
or, if such stock is not listed on any such exchange, the highest closing bid
quotation with respect to a share of such stock during the 30-day period
immediately prior to and including the date in question on the National
Association of Securities Dealers Automated Quotation System or any comparable
value system then in use, or if no such quotations are available, the fair
market value on the date in question of a share of such stock as determined by
the affirmative vote of a majority of the Continuing Directors of the Board of
Directors in good faith; and

                   (2)  in the case of property other than cash or stock, the
fair market value of such property on the date in question is determined by an
affirmative vote of a majority of the Continuing Directors of the Board of
Directors in good faith.

              3I.  "Group Acting in Concert" shall mean persons seeking to
combine or pool their voting or other interests in the securities of the
Corporation for a common purpose, pursuant to any contract, understanding or
relationship, agreement or other arrangement, whether written, oral or
otherwise, or any "group of persons" as defined under Section 13(d) of the 1934

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<PAGE>

Act (or any subsequent provisions replacing such Act or rules or regulations
promulgated thereunder).  When persons act together for any such purpose, their
group is deemed to have acquired their stock.

              3J.  In the event of any Business Combination in which the
Corporation survives, the phrase "consideration other than cash to be received"
as used in this Article V shall include the shares of common stock and/or the
shares of any other class of outstanding Voting Stock retained by the holders of
such shares.

              3K.  "Voting Stock" shall mean the outstanding shares of capital
stock of the Corporation entitled, at the time, to vote generally in the
election of Directors.

              3L.  "Grandfathered Percentage" shall mean , with respect to any
Grandfathered Person, the percentage of the voting power of the then outstanding
shares of Voting Stock that such Grandfathered Person beneficially owns as of
the close business on the date of the closing of the initial public offering of
shares of common stock of the Corporation in the fall of 1993 plus an additional
two (2) percentage points; provided, however, that in the event the underwriters
exercise their over-allotment option in connection with this initial public
offering of shares of common stock, the Grandfathered Percentage shall, from and
after the closing of such over-allotment option, mean, with respect to any
Grandfathered Person, the percentage of the voting power of the then outstanding
shares of Voting Stock that such Grandfathered Person beneficially owns as of
the close of business on the date of the closing of the over-allotment option
plus an additional two (2) percentage points; and provided, further, that, in
the event of any Grandfathered Person shall sell, transfer or otherwise dispose
of any outstanding shares of Voting Stock after the close of business on the
date of the closing of the initial public offering of the Corporation's common
stock in the fall of 1993, the Grandfathered Percentage shall, subsequent to
such sale, transfer or disposition, mean, with respect to such Grandfathered
Person, the lesser of (i) the Grandfathered Percentage as in effect immediately
prior to such sale, transfer, or disposition or (ii) the percentage of the
voting power of the then outstanding shares of Voting Stock that such
Grandfathered Person beneficially owns immediately following such sale, transfer
or disposition plus an additional two (2) percentage points.

              3M.  "Grandfathered Person" shall mean any Person who or which,
together with all Affiliates and Associates of such Person, is, as of the close
of business on the date of the closing of the initial public offering of shares
of common stock of the Corporation in the fall of 1993, the beneficial owner of
15% or more of the voting power of the then outstanding Voting Stock at such
time.

              3N.  The term "voting power" shall mean, with respect to each
outstanding share of capital stock of the Corporation, the number of votes of
which a holder of such share shall be entitled, at the time, to vote generally
in the election of the Directors.

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<PAGE>

                        PART D.  Powers of the Board of Directors.

    A majority of the Directors of the Corporation, unless there is an
Interested Stockholder, in which case a majority of the Continuing Directors
then in office, shall have the power to determine for the purposes of this
Article V, on the basis of information known to them after reasonable inquiry,
(i) whether a person is an Interested Stockholder, (ii) the number or percentage
of shares of Voting Stock or other equity securities beneficially owned by any
person, (iii) whether a person is an Affiliate or Associate of, or is affiliated
or associated with, another person, (iv) whether the assets which are the
subject of any Business Combination have, or the consideration to be received
for the issuance or transfer of securities by the Corporation or any Subsidiary
in any Business Combination, has, an aggregate Fair Market Value of $5,000,000
or more, (v) whether the requirements of Part B of this Article V have been met
with respect to any Business Combination, and (vi) any other matters of
interpretation arising under this Article V.  The good faith determination by
the affirmative vote of a majority of the Directors, or, if there is an
Interested Stockholder, by the affirmative vote of a majority of the Continuing
Directors then in office, on such matters shall be conclusive and binding for
all purposes of this Article V.

       PART E.  No Effect on Fiduciary Obligations of Interested Stockholders.

    Nothing contained in this Article V shall be construed to relieve any
Interested Stockholder from any fiduciary obligation imposed by law.

                                     ARTICLE VI.

                                  STOCKHOLDER ACTION
                                           
         Any action required or permitted to be taken by the stockholders of
the Corporation must be effected at a duly called annual or special meeting of
such holders or by a consent in writing signed by the holders of all of the
outstanding shares authorized to vote at such meeting.  Except as otherwise
required by law, special meetings of the stockholders of the Corporation may be
called only by (i) the Board of Directors pursuant to a resolution approved by
the affirmative vote of a majority of the Directors then in office, (ii) the
Chairman of the Board, if one is elected, or (iii) the President; provided,
however, that, if at the time of any such call there is an Interested
Stockholder, such call shall also require the affirmative vote of a majority of
the Continuing Directors then in office.  Only those matters set forth in the
notice of the special meeting may be considered or acted upon at a special
meeting of stockholders of the Corporation, unless otherwise provided by law. 
Advance notice of any matters which stockholders intend to propose for action at
an annual meeting shall be given in the manner provided in the By-Laws.   

                                     17

<PAGE>


                                     ARTICLE VII.

                                      DIRECTORS
                                           
         1.   General. All power of the Corporation shall be exercised by or
under the direction of the Board of Directors except as otherwise provided
herein or required by law.

         2.   Election of Directors.  Election of Directors need not be by
written ballot unless the By-Laws of the Corporation shall so provide.

         3.   Number, Election and Terms.

              3A.  Except as otherwise fixed pursuant to the provisions of
Article IV hereof relating to the rights of the holders of any class or series
of preferred stock to elect Directors, the number of Directors of the
Corporation shall be fixed exclusively by resolution duly adopted from time to
time by the affirmative vote of at least two-thirds of  the Board of Directors. 
The Directors, other than those who may be elected by the holders of any class
or series of preferred stock, shall be classified, with respect to the time for
which they severally hold office, into two classes, as nearly equal in number as
possible as determined by the Board of Directors, with one class to be elected
annually.

              3B.  Commencing at the effective time of the merger of Strategic
Diagnostics Inc. ("SDI") and EnSys Environmental Products, Inc. ("EnSys"), with
the Corporation as the surviving corporation, and continuing through the 1998
annual meeting of stockholders of the Corporation, the Board of Directors shall
consist of seven (7) members.  The initial Board of Directors shall be elected
as follows:  EnSys and SDI will each select three (3) members of the Board of
Directors and the remaining member of the Board of Directors will be selected by
The Perkin-Elmer Corporation (the "Perkin-Elmer Corporation").  The Directors of
the Corporation shall hold office as follows: the Class I Directors shall hold
office for a term expiring at the 1997 annual meeting of the stockholders and
the Class II Directors shall hold office for a term expiring at the 1998 annual
meeting of stockholders, with the members of each class to hold office until
their respective successors are duly elected and qualified.  At each annual
meeting of the stockholders of the Corporation, Directors elected to succeed
those whose terms are expiring at that meeting shall be elected to hold office
for a term expiring at the annual meeting of stockholders held in the second
year following the year of their election and until their respective successors
are duly elected and qualified.  No decrease in the number of directors shall
shorten the term of any incumbent director.

         4.   Stockholder Nominations of Director Candidates.  Except as
otherwise fixed pursuant to the provisions of Article IV hereof relating to the
rights of the holders of any class of series of preferred stock to elect
Directors, advance notice of nominations for the election of Directors, other
than by the Board of Directors or a committee thereof, shall be given in the
manner provided in the By-Laws.  Notwithstanding the foregoing, all Class I
Directors

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holding office at the time of the 1997 annual meeting shall automatically be
nominated, subject to such director's consent, to serve an additional two (2)
year term expiring at the 1999 annual meeting of the stockholders of the
Corporation and all Class II Directors holding office at the time of the 1998
annual meeting shall automatically be nominated, subject to such director's
consent, to serve an additional two (2) year term expiring at the 2000 annual
meeting of the stockholders of the Corporation.

         5.   Vacancies and Newly Created Directorships.  Except as otherwise
fixed pursuant to the provisions of Article IV hereof relating to the rights of
the holders of any class or series of preferred stock to elect Directors, any
vacancy occurring in the Board of Directors, including any vacancy created by
reason of a newly created directorship resulting in an increase in the number of
directors or any vacancy resulting from death, resignation, disqualification,
removal or other causes, shall be filled solely by the affirmative vote of a
majority of the remaining Directors then in office, if a quorum is present;
provided, however, that, if there is an Interested Stockholder at the time of
such vote, the filling of such vacancy shall also require the affirmative vote
of a majority of the Continuing Directors then in office.  Notwithstanding
anything contained herein to the contrary, any Director that voluntarily leaves
office may vote on his or her replacement.  Any Director appointed in accordance
with the preceding sentence shall hold office for the remainder of the full term
of the class of Directors in which the new directorship was created or the
vacancy occurred and until such Director's successor shall have been duly
elected and qualified.  When the number of Directors is increase or decreased,
the Board of Directors shall determine the class or classes to which the
increased or decreased number of Directors shall be apportioned.  In the event
of a vacancy in the Board of Directors, the remaining Directors, except as
otherwise provided by law, may exercise the powers of the full Board of
Directors until the vacancy is filled.

         6.   Removal.  Except as otherwise fixed pursuant to the provisions of
Article IV hereof relating to the rights of the holders of any class or series
of preferred stock to elect Directors, any Director (including persons elected
by Directors to fill vacancies in the Board of Directors) may be removed from
office only with cause and by the affirmative vote of at least two-thirds of the
total votes which would be eligible to be cast by stockholders in the election
of such Director at a duly constituted meeting of stockholders called expressly
for such purpose.  A Director may not be removed from office without cause.  At
least 30 days prior to any meeting of stockholders at which it is proposed that
any Director be removed from office, written notice shall be sent to the
Director whose removal will be considered at the meeting.

                                    ARTICLE VIII.

                               LIMITATION OF LIABILITY

         A Director of the Corporation shall not be personally liable to the
Corporation or its stockholders for monetary damages for breach of fiduciary
duty as a Director, except for liability (i) for any breach of the Director's
duty of loyalty to the Corporation or its stockholders, (ii) for acts or
omissions not in good faith or which involve intentional misconduct or a knowing

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violation of law, (iii) under Section 174 of the General Corporation Law of 
Delaware, or (iv) for any transaction from which the Director derived an
improper personal benefit.  If the General Corporation Law of Delaware is
amended after the effective date of this Certificate of Incorporation to
authorize corporate action further eliminating or limiting the personal
liability of directors, then the liability of a Director of the Corporation
shall be eliminated or limited to the fullest extent permitted by the General
Corporation Law of Delaware, as so amended.

         Any repeal or modification of this Article VIII (i) by the
stockholders of the Corporation, or (ii) by an amendment to the General
Corporation Law of Delaware shall not adversely affect any right or protection
existing at the time of such repeal or modification with respect to any acts or
omissions occurring either before or after such repeal or modification of a
person serving as a Director at the time of such repeal or modification.

                                    ARTICLE IX.                             

                     STANDARDS FOR BOARD OF DIRECTORS' EVALUATION
                                OF OFFERS OR PROPOSALS
                                           
         The Board of Directors of the Corporation, when evaluating any offer
or proposal of any person to (i) make a tender or exchange offer for any equity
security of the Corporation or any subsidiary, (ii) merge or consolidate the
Corporation or any subsidiary with another person, or (iii) purchase or
otherwise acquire all or substantially all of the properties and assets of the
Corporation or any subsidiary, may, in connection with the exercise of its
judgment in determining what is in the best interests of the Corporation and its
stockholders, give due consideration to all relevant factors, including without
limitation, (a) the social and economic effects of acceptance of such offer or
proposal on the employees of the Corporation and its subsidiaries, the
suppliers, creditors, and customers of the Corporation and its subsidiaries, and
the state, region, and communities in which the Corporation and its subsidiaries
operate and are located, and (b) the long-term and short-term interests of the
Corporation and its stockholders, including the possibility that these interests
may be best served by the continued independence of the Corporation.

                                      ARTICLE X.     

                                 AMENDMENT OF BY-LAWS
                                           
         The Board of Directors shall have the power to adopt, alter, amend and
repeal the By-Laws of the Corporation.  Any By-Laws of the Corporation adopted
by the Directors under the powers conferred hereby may be altered, amended or
repealed by the Directors or the stockholders.  Notwithstanding the foregoing or
any other provisions of this Certificate of Incorporation or the By-Laws of the
Corporation to the contrary, such action by the Board of Directors shall require
the affirmative vote of at least two-thirds of the Directors then in office. 
Notwithstanding the foregoing or any other provisions of this Certificate of
Incorporation or the By-Laws of the Corporation to the contrary, any action by
the stockholders to alter, amend or

                                     20

<PAGE>

repeal the By-Laws of the Corporation shall require the affirmative vote of at
least two-thirds of the total votes eligible to be cast by stockholders with
respect to such alteration, amendment or repeal, voting together as a single
class, at a duly constituted meeting of stockholders called expressly for
such purpose.

                                    ARTICLE XI.    

                      AMENDMENT OF CERTIFICATE OF INCORPORATION
                                           
         The Corporation reserves the right to repeal, alter or amend this
Certificate of Incorporation in the manner now or hereafter prescribed by
statute and this Certificate of Incorporation, and all rights conferred upon
stockholders herein are granted subject to this reservation.  No repeal,
alteration or amendment of this Certificate of Incorporation shall be made
unless the same is first approved by the Board of Directors of the Corporation
pursuant to a resolution adopted by the affirmative vote of a majority of the
Directors then in office, and thereafter approved by the stockholders.

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