<PAGE>

                                                                    EXHIBIT 10.2

================================================================================

                          INSITUFORM TECHNOLOGIES, INC.

                       -----------------------------------

                                FOURTH AMENDMENT
                           Dated as of March 12, 2004

                                       to

                            NOTE PURCHASE AGREEMENTS
                          Dated as of February 14, 1997

                       -----------------------------------

                    Re: $110,000,000 Senior Notes, Series A,
                              Due February 14, 2007

================================================================================

<PAGE>

                   FOURTH AMENDMENT TO NOTE PURCHASE AGREEMENT

         THIS FOURTH AMENDMENT dated as of March 12, 2004 (the or this "Fourth
Amendment") to the Note Purchase Agreements dated as of February 14, 1997, is
between INSITUFORM TECHNOLOGIES, INC., a Delaware corporation (the "Company"),
and each of the institutions which is a signatory to this Fourth Amendment
(collectively, the "Noteholders").

                                    RECITALS:

         A.       The Company has entered into separate and several Note
Purchase Agreements dated as of February 14, 1997 with the institutional
investors named in each Note Purchase Agreement (as heretofore amended, the
"Note Agreements"), pursuant to which the Company has issued its 7.88% Senior
Notes, Series A, due February 14, 2007, in the aggregate principal amount of
$110,000,000 (the "Notes").

         B.       The Company and the Noteholders now desire to amend the Note
Agreements and the Notes in the respects, but only in the respects, hereinafter
set forth in order to reflect certain agreements between the Company and the
Noteholders.

         C.       Capitalized terms used herein shall have the respective
meanings ascribed thereto in the Note Agreements unless herein defined or the
context shall otherwise require.

         D.       All requirements of law have been fully complied with and all
other acts and things necessary to make this Fourth Amendment a valid, legal and
binding instrument according to its terms for the purposes herein expressed have
been done or performed.

         NOW, THEREFORE, upon the full and complete satisfaction of the
conditions precedent to the effectiveness of this Fourth Amendment set forth in
Section 3.1 hereof, and in consideration of good and valuable consideration the
receipt and sufficiency of which is hereby acknowledged, the Company and the
Noteholders do hereby agree as follows:

SECTION 1. AMENDMENTS TO NOTE AGREEMENTS AND THE NOTES.

         Section 1.1. Amendment to Interest Rate on the Series A Notes. (a) Upon
the Effective Date (as defined in Section 3.1 of this Fourth Amendment), the
rate of interest payable on each outstanding Note shall be changed from 7.88%
per annum to the Applicable Rate. As used in the Note Agreements and the Notes
"Applicable Rate" shall mean (i) 8.63% per annum from and after the Effective
Date to and including March 31, 2005, (ii) 8.38% per annum from and after April
1, 2005 to and including March 31, 2006, and (iii) 7.88% per annum from and
after April 1, 2006 to maturity.

         (b)      From and after the Effective Date, (i) each reference to
"7.88%" in the Note Agreements shall be deleted (except as used in the term
"Applicable Rate"), and (ii) the form of Note attached as Exhibit 1 to the Note
Agreements, shall be and is hereby amended in its entirety to read as set forth
in Exhibit 1 to this Fourth Amendment.

<PAGE>

         Section 1.2. Amendment to Section 9. (Additional Financial Covenants).
Section 9 of the Note Agreements shall be and is hereby amended by the addition
of a new Section 9.9 which shall read as follows:

                           Section 9.9. Additional Covenants. If the Bank Credit
                  Agreement is amended, replaced or renewed after the Effective
                  Date to and including the Transition Date in a manner which
                  makes the financial covenants set forth therein more
                  restrictive on the Company and its Subsidiaries than the
                  financial covenants contained in Section 10 of this Agreement
                  or to add additional financial covenants or to make the
                  existing Bank Credit Agreement covenants more restrictive than
                  the financial covenants in the Bank Credit Agreement on the
                  Effective Date, then such more restrictive financial covenants
                  and any related definitions (the "Additional Financial
                  Covenants") shall automatically be deemed to be incorporated
                  into Section 7.2(a) and Section 10 of this Agreement by
                  reference and Section 11(c) shall be deemed to be amended to
                  include such Additional Financial Covenants from the time such
                  Additional Financial Covenants become binding upon the Company
                  until the Transition Date. No amendment or modification of the
                  Additional Financial Covenants shall result in any change in
                  the covenants expressly set forth in Section 10 which shall at
                  all times remain in effect. Promptly but in no event more than
                  5 Business Days following the execution of any new Bank Credit
                  Agreement, or any amendment to the Bank Credit Agreement, the
                  Company shall furnish each holder of the Notes with a copy of
                  such agreement. In no event shall the Company or any
                  Subsidiary provide any collateral or other security to secure
                  Indebtedness under the Bank Credit Agreement on or prior to
                  the Transition Date.

         Section 1.3. Amendment to Section 10.2 (Fixed Charges Coverage Ratio).
Section 10.2 of the Note Agreements shall be and is hereby amended in its
entirety to read as follows:

                           "Section 10.2. Fixed Charges Coverage Ratio. The
                  Company will as at the end of each fiscal quarter keep and
                  maintain the ratio of Consolidated Cash Flow Available for
                  Fixed Charges for the four consecutive fiscal quarter period
                  ending at such date to Consolidated Fixed Charges for such
                  four consecutive fiscal quarter period at not less than 2.00
                  to 1 for the fiscal quarters ended on or prior to September
                  30, 2003, 1.25 to 1 for the fiscal quarters ended December 31,
                  2003, and March 31 2004, 1.20 to 1 for the fiscal quarters
                  ending June 30, 2004 and September 30, 2004 and 1.7 to 1 for
                  the fiscal quarters ending December 31, 2004 and March 31,
                  2005 and 2.50 to 1 for each quarter ending thereafter."

                                      -2-

<PAGE>

         Section 1.4. Amendment to Section 10.4 (Priority Debt). Section 10.4 of
the Note Agreements shall be and is hereby amended in its entirety to read as
follows:

                           "Section 10.4. Priority Debt. The Company will not,
                  and will not permit any Subsidiary to create, issue, assume,
                  guarantee or otherwise incur or in any manner become liable in
                  respect of any Priority Debt unless at the time of creation,
                  issuance, assumption, guarantee or incurrence thereof and
                  after giving effect thereto and to the application of the
                  proceeds thereof: (a) no Specified Default or Event of Default
                  would exist and (b) the aggregate amount of all Priority Debt
                  would not exceed $10,000,000 on or prior to the Transition
                  Date and 10% of Consolidated Adjusted Net Worth thereafter
                  determined as of the end of the immediately preceding fiscal
                  quarter. In addition from and after the Effective Date to and
                  including the Transition Date, no Priority Debt shall be
                  incurred except by foreign Subsidiaries of the Company under
                  agreements for which the Company shall have no liability
                  except pursuant to an unsecured Guaranty of such Subsidiary
                  obligation.

                           Any Person which becomes a Subsidiary after the date
                  of this Agreement, shall, for all purposes of this SECTION
                  10.4, be deemed to have created, issued, assumed, guaranteed
                  or incurred, at the time it becomes a Subsidiary, all Priority
                  Debt of such Person existing immediately after it becomes a
                  Subsidiary."

         Section 1.5. Amendment to Section 10.6 (Restricted Payments). Section
10.6 of the Note Agreements shall be and is hereby amended in its entirety to
read as follows:

                           "Section 10.6. Restricted Payments. From and after
                  the Effective Date to and including the Transition Date, the
                  Company will not:

                           (1)      declare or pay any dividends, either in cash
                  or property, on any shares of its capital stock of any class
                  (except dividends or other distributions payable solely in
                  shares of common stock of the Company),

                           (2)      directly or indirectly, or through any
                  Subsidiary or through any Affiliate of the Company, purchase,
                  redeem or retire any shares of its capital stock of any class
                  or any warrants, rights or options to purchase or acquire any
                  shares of its capital stock (other than in exchange for or out
                  of the net cash proceeds to the Company from the substantially
                  concurrent issue or sale of shares of common stock of the
                  Company or warrants, rights or options to purchase or acquire
                  any shares of its common stock), or

                                      -3-

<PAGE>

                           (3)      make any other payment or distribution,
                  either directly or indirectly or through any Subsidiary, in
                  respect of its capital stock.

                           After the Transition Date, the Company will not make
                  such declarations or payments of dividends, purchases,
                  redemptions or retirements of capital stock and warrants,
                  rights or options and all such other payments or distributions
                  ("Restricted Payments") if: (i) immediately prior to the
                  making of any Restricted Payment, a Specified Default or Event
                  of Default exists, (ii) immediately after giving effect to the
                  making of any Restricted Payment, a Specified Default or Event
                  of Default would exist, and (iii) immediately after giving
                  effect to the making of any Restricted Payment, the Company
                  could not incur at least $1.00 of additional Indebtedness
                  pursuant to SECTION 10.3."

         Section 1.6. Amendment to Section 10. Section 10 of the Note Agreements
shall be and is hereby amended by the addition thereto of new covenants
immediately following Section 10.8 which shall read as follows:

                           Section 10.9. Prepayment and Purchase of Notes.
                  Except as provided in Section 8.1 of this Agreement, from and
                  after the Effective Date to and including the Transition Date,
                  the Company will not make any optional prepayment of the Notes
                  pursuant to Section 8.2 or otherwise prepay or purchase any
                  Notes from any holder unless concurrently therewith, the
                  Company shall prepay or purchase, as the case may be, a pro
                  rata principal amount of the 2003 Notes.

                           Section 10.10. Capital Expenditures. The Company will
                  not make any Capital Expenditures, in the aggregate for the
                  period beginning January 1, 2004 to and including the
                  Transition Date which, net of proceeds realized by the Company
                  from the routine sale of fixed assets in the ordinary course
                  of business during such period, exceed $40,000,000; provided,
                  that such sales of fixed assets comply with the requirements
                  of Section 10.7(b) hereof and the proceeds therefrom are
                  applied in the manner described in Section 10.7(b)(iii)(y)(A).

                           Section 10.11. Acquisitions. Prior to the Transition
                  Date, the Company will not, and will not permit any Subsidiary
                  to, make any acquisition of stock or other equity interest in
                  any Person or all or substantially all of the assets of any
                  Person except for consideration which consists solely of
                  common stock of the Company and so long as at the time of such
                  acquisition and after giving effect thereto no Default or
                  Event of Default exists."

                                      -4-

<PAGE>

         Section 1.7. Amendment to Section 11(f) (Events of Default). Clause
(ii) of Section 11(f) of the Note Agreements shall be and is hereby amended in
its entirety to read as follows:

                  "(ii) the Company or any Subsidiary is in default in the
                  performance of or compliance with any term of any evidence of
                  any Indebtedness in an aggregate outstanding principal amount
                  of at least $5,000,000 or of any mortgage, indenture or other
                  agreement relating thereto or any other condition exists, and
                  as a consequence of such default or condition such
                  Indebtedness has become, or has been declared (or one or more
                  Persons are entitled to declare such Indebtedness to be), due
                  and payable before its stated maturity or before its regularly
                  scheduled dates of payment; provided that from and after the
                  Effective Date to and including the Transition Date, any Event
                  of Default arising under this Section 11(f)(ii) shall continue
                  regardless of any waiver or cure of the default under the
                  mortgage, indenture or other agreement which gave rise to such
                  Event of Default hereunder, or"

         Section 1.8. Amendment to Schedule B (Definitions - Addition of New
Definitions). Schedule B of the Note Agreements is hereby amended by the
addition thereto of the following new definitions which shall appear in
alphabetical order therein and which shall read as follows:

                  "Applicable Rate" has the meaning set forth in Section 1.1 of
                  the Fourth Amendment.

                  "Capital Expenditure" means an expenditure for an asset that
                  must be depreciated or amortized under GAAP, for goodwill, or
                  for any asset that under GAAP must be treated as a capital
                  asset, including payments under Capital Leases. An expenditure
                  for purposes of this definition includes any deferred or
                  seller financed portion of the purchase price of an asset and
                  the original capitalized amount of a Capital Lease. Capital
                  Expenditures shall exclude expenditures by the Company and its
                  Subsidiaries for equipment related to its tunnel business
                  which is acquired by the Company or any Subsidiary in
                  connection with the performance of any construction contract
                  which provides for the total recovery of the purchase price of
                  such equipment from the customer over the life of the
                  contract.

                  "Effective Date" has the meaning set forth in Section 3.1 of
                  the Fourth Amendment.

                  "Fourth Amendment" means the Fourth Amendment to this
                  Agreement dated as of March 12, 2004 among the Company and the
                  holders of the Notes.

                                      -5-

<PAGE>

                  "Transition Date" means March 31, 2005; provided that if any
                  Default or Event of Default exists under this Agreement on
                  March 31, 2005, then the Transition Date shall not occur until
                  such time as such Default or Event of Default shall have been
                  waived by the requisite percentage of the holders of the
                  Notes.

                  "2003 Notes" means the Senior Notes due April 24, 2013 of the
                  Company.

SECTION 2. REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

         Section 2.1. To induce the Noteholders to execute and deliver this
Fourth Amendment, the Company represents and warrants (which representations
shall survive the execution and delivery of this Fourth Amendment) to the
Noteholders that:

                  (a)      this Fourth Amendment has been duly authorized,
         executed and delivered by it and this Fourth Amendment constitutes the
         legal, valid and binding obligation, contract and agreement of the
         Company enforceable against it in accordance with its terms, except as
         enforcement may be limited by bankruptcy, insolvency, reorganization,
         moratorium or similar laws or equitable principles relating to or
         limiting creditors' rights generally;

                  (b)      the Note Agreements and the Notes, as amended by this
         Fourth Amendment, constitute the legal, valid and binding obligations,
         contracts and agreements of the Company enforceable against it in
         accordance with their terms, except as enforcement may be limited by
         bankruptcy, insolvency, reorganization, moratorium or similar laws or
         equitable principles relating to or limiting creditors' rights
         generally;

                  (c)      the execution, delivery and performance by the
         Company of this Fourth Amendment (i) has been duly authorized by all
         requisite corporate action and, if required, shareholder action, (ii)
         does not require the consent or approval of any governmental or
         regulatory body or agency, and (iii) will not (A) violate (1) any
         provision of law, statute, rule or regulation or its certificate of
         incorporation or bylaws, (2) any order of any court or any rule,
         regulation or order of any other agency or government binding upon it,
         or (3) any provision of any material indenture, agreement or other
         instrument to which it is a party or by which its properties or assets
         are or may be bound, or (B) result in a breach or constitute (alone or
         with due notice or lapse of time or both) a default under any
         indenture, agreement or other instrument referred to in clause
         (iii)(A)(3) of this Section 2.1(c), other than any violation, breach or
         default which individually or in the aggregate could not reasonably be
         expected to have a Material Adverse Effect;

                  (d)      as of the date hereof and after giving effect to this
         Fourth Amendment, no Default or Event of Default has occurred which is
         continuing;

                  (e)      the unaudited financial statements of the Company for
         the fiscal year ended December 31, 2003 furnished to you do not, nor
         does any written statement

                                      -6-

<PAGE>

         furnished by the Company to you in connection with the execution and
         delivery of this Fourth Agreement, contain any untrue statement of a
         material fact or omit to state any material fact necessary to make the
         statements contained therein not misleading in light of the
         circumstances under which they were made. There is no fact known to the
         Company which the Company has not disclosed to you in writing which
         could reasonably be expected to have a Material Adverse Effect; and

                  (f)      The Company has not paid any consideration to any
         holder of indebtedness of the Company in connection with the
         transactions contemplated by this Fourth Amendment, except for the
         legal fees of counsel to the holders of such indebtedness and
         consideration paid to the holders of the Senior Notes due April 24,
         2013 which is identical to the consideration to be paid to the holders
         of the Notes.

SECTION 3. CONDITIONS TO EFFECTIVENESS OF THIS FOURTH AMENDMENT.

         Section 3.1. This Fourth Amendment shall become effective when each of
the following conditions has been satisfied:

                  (a)      executed counterparts of this Fourth Amendment, duly
         executed by the Company and the holders of at least 66-2/3% of the
         outstanding principal of the Notes, shall have been delivered to the
         Noteholders;

                  (b)      executed copies of a consent to this Agreement shall
         have been duly executed by the Subsidiaries which are parties to the
         Subsidiary Guaranties;

                  (c)      the representations and warranties of the Company set
         forth in Section 2 hereof shall be true and correct on and with respect
         to the date hereof and a certificate of a Responsible Officer
         certifying the same shall have been delivered to the Noteholders;

                  (d)      the First Amendment dated as of March 12, 2004 to the
         2003 Note Purchase Agreements shall have been duly executed and
         delivered by the requisite percentage of the noteholders thereunder
         required to approve such amendment and such agreement shall be in form
         and substance satisfactory to each Noteholder;

                  (e)      the Company shall have paid a fee to each Noteholder
         in an amount equal to .25% of the outstanding principal amount of the
         Notes held by such Noteholder;

                  (f)      Thompson Coburn LLP, counsel for the Company, shall
         have delivered a legal opinion, dated as of the effective date of this
         Fourth Amendment, in form and substance reasonably satisfactory to the
         Noteholders and their special counsel to the effect that this Fourth
         Amendment constitutes the legal, valid and binding obligation of the
         Company;

                  (g)      the Company shall have delivered a copy of the
         amended and restated Bank Credit Agreement which provides for a
         revolving credit facility and the issuance of letters of credit for the
         benefit of the Company and its Subsidiaries; and

                                      -7-

<PAGE>

                  (h)      the Company shall have paid the fees, costs, expenses
         and disbursements of Chapman and Cutler LLP, special counsel to the
         Noteholders, incurred in connection with the consummation of the
         transactions contemplated by this Fourth Amendment.

Upon receipt of all of the foregoing, this Fourth Amendment shall become
effective. Delivery of this Fourth Amendment to the Company, duly executed by
the holders of at least 66-2/3% of the outstanding principal amount of the
Notes, shall acknowledge satisfaction of the foregoing conditions. The date upon
which this Fourth Amendment becomes effective is herein referred to as the
"Effective Date." The Company shall give written notice to the Noteholders of
the Effective Date, confirming the date upon which the increased interest rate
referred to in Section 1.1 hereof shall begin to accrue.

SECTION 4. MISCELLANEOUS.

         Section 4.1. Automatically, and without any further action on the part
of the Company or any holder of a Note, on the Effective Date, the Notes shall
be deemed to be amended to reflect the change in interest rate set forth in
Section 1.1 of this Fourth Amendment; provided, however, that if any holder of a
Note elects to surrender its Note (an "Existing Note") to the Company for
cancellation and the issuance of a new note reflecting such change in interest
rate (a "New Note"), the Company shall issue a New Note to such holder within 5
business days of receipt of the Existing Note surrendered therefor, such New
Note to be dated the date to which interest has been paid on the Existing Note
surrendered therefor and such New Note shall be payable on the same dates as set
forth in the Existing Note surrendered therefor.

         Section 4.2. The Company acknowledges and agrees that by agreeing to
the amendments of the Note Agreements set forth herein, the Noteholders shall
not be deemed to have waived any rights as on account of any Default or Event of
Default which may at any time hereafter exist under the Note Agreements, which
rights are hereby expressly reserved by the holders of the Notes.

         Section 4.3. This Fourth Amendment shall be construed in connection
with and as part of the Note Agreements, and except as modified and expressly
amended by this Fourth Amendment, all terms, conditions and covenants contained
in the Note Agreements and the Notes are hereby ratified and shall be and remain
in full force and effect.

         Section 4.4. Any and all notices, requests, certificates and other
instruments executed and delivered after the execution and delivery of this
Fourth Amendment may refer to the Note Agreements without making specific
reference to this Fourth Amendment but nevertheless all such references shall
include this Fourth Amendment unless the context otherwise requires.

         Section 4.5. The descriptive headings of the various Sections or parts
of this Fourth Amendment are for convenience only and shall not affect the
meaning or construction of any of the provisions hereof.

         Section 4.6. This Fourth Amendment shall be governed by and construed
in accordance with Illinois law.

                                      -8-

<PAGE>

         Section 4.7. The execution hereof by you shall constitute a contract
between us for the uses and purposes hereinabove set forth, and this Fourth
Amendment may be executed in any number of counterparts, each executed
counterpart constituting an original, but all together only one agreement.

                                          INSITUFORM TECHNOLOGIES, INC.

                                          By /s/ CHRISTIAN G. FARMAN
                                             -----------------------------------
                                             Its Vice President, Chief Financial
                                                 -------------------------------
                                                 Officer and Assistant Secretary
                                                 -------------------------------


                                      -9-

<PAGE>
Accepted and agreed to as of the date first written above:

                                          THE NORTHWESTERN MUTUAL LIFE INSURANCE
                                             COMPANY

                                          By /s/ DAVID A. BARRAS
                                             -----------------------------------
                                                 David A. Barras
                                             Its Authorized Representative


                                          RELIASTAR LIFE INSURANCE COMPANY,
                                             successor by merger to Northern
                                             Life Insurance Company

                                          RELIASTAR LIFE INSURANCE COMPANY,
                                             successor by merger to ReliaStar
                                             United Services Life Insurance
                                             Company

                                          RELIASTAR LIFE INSURANCE COMPANY OF
                                             NEW YORK

                                          RELIASTAR LIFE INSURANCE COMPANY

                                          By: ING Investment Management LLC, as
                                              Agent

                                              By /s/ JAMES V. WITTICH
                                                 -------------------------------
                                                     James V. Wittich
                                                 Its SVP

                                          ACE PROPERTY & CASUALTY INSURANCE
                                             COMPANY

                                          By: Columbia Management Advisors,
                                              Inc., as agent

                                              By /s/ RICHARD A. HEGWOOD
                                                 -------------------------------
                                                     Richard A. Hegwood
                                                 Its Senior Vice President


                                          THE SECURITY FINANCIAL LIFE INSURANCE
                                             CO.

                                              By /s/ KEVIN W. HAMMOND
                                                 -------------------------------
                                                     Kevin W. Hammond
                                                 Its Vice President
                                                     Chief Investment Officer


                                          PRINCIPAL LIFE INSURANCE COMPANY

                                          By: Principal Global Investors, LLC,
                                              a Delaware limited liability
                                              company, its Authorized Signatory

                                              By /s/
                                                 -------------------------------
                                                 Its Counsel

                                              By /s/
                                                 -------------------------------
                                                 Its Counsel


                                          JEFFERSON-PILOT LIFE INSURANCE COMPANY

                                          By /s/ JAMES E. MCDONALD, JR.
                                             -----------------------------------
                                                  James E. McDonald, Jr.
                                             Its:

                                          JEFFERSON PILOT FINANCIAL INSURANCE
                                          COMPANY
                                             (successor by merger to Alexander
                                             Hamilton Life Insurance Company of
                                             America)

                                          By /s/ JAMES E. MCDONALD, JR.
                                             -----------------------------------
                                                  James E. McDonald, Jr.
                                             Its:


                                          ALLSTATE LIFE INSURANCE COMPANY

                                          By /s/ JERRY D. ZINKULA
                                             -----------------------------------

                                          By /s/ ROBERT B. BODETT
                                             -----------------------------------
                                             Authorized Signatories


                                          CONNECTICUT GENERAL LIFE INSURANCE
                                             COMPANY


                                          By: CIGNA Investments, Inc.

                                              By /s/ DEBRA J. HEIGHT
                                                 -------------------------------
                                                     Debra J. Height
                                                 Its Managing Director


                                          LIFE INSURANCE COMPANY OF NORTH
                                             AMERICA

                                          By: CIGNA Investments, Inc.

                                              By /s/ DEBRA J. HEIGHT
                                                 -------------------------------
                                                     Debra J. Height
                                                 Its Managing Director


                                          CONNECTICUT GENERAL LIFE INSURANCE
                                             COMPANY, on behalf of one or more
                                             separate accounts

                                          By: CIGNA Investments, Inc.

                                              By /s/ DEBRA J. HEIGHT
                                                 -------------------------------
                                                     Debra J. Height
                                                 Its Managing Director




<PAGE>

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED,
AND MAY NOT BE TRANSFERRED IN VIOLATION OF SUCH ACT.

                          INSITUFORM TECHNOLOGIES, INC.

               7.88% SENIOR NOTE, SERIES A, DUE FEBRUARY 14, 2007

No. [________________]                                                    [Date]
$[__________________]                                           PPN 457 667 A* 4

         FOR VALUE RECEIVED, the undersigned, INSITUFORM TECHNOLOGIES, INC.
(herein called the "Company"), a corporation organized and existing under the
laws of the State of Delaware, hereby promises to pay to [____________________],
or registered assigns, the principal sum of [_____________________] DOLLARS on
February 14, 2007, with interest (computed on the basis of a 360-day year of
twelve 30-day months) (a) on the unpaid balance thereof at the Applicable Rate
(as defined in the Note Purchase Agreements referred to below) from the date
hereof, payable semiannually, on the fourteenth day of February and August in
each year, commencing with August 14, 1997 until the principal hereof shall have
become due and payable, and (b) to the extent permitted by law on any overdue
payment (including any overdue prepayment) of principal, any overdue payment of
interest and any overdue payment of any Make-Whole Amount (as defined in the
Note Purchase Agreements referred to below), payable semiannually as aforesaid
(or, at the option of the registered holder hereof, on demand), at a rate per
annum from time to time equal to the greater of (i) 2% over the Applicable Rate
or (ii) 2% over the rate of interest publicly announced by JP Morgan Chase Bank
from time to time in New York, New York as its "base" or "prime" rate.

         Payments of principal of, interest on and any Make-Whole Amount with
respect to this Note are to be made in lawful money of the United States of
America at Chicago, Illinois or at such other place as the Company shall have
designated by written notice to the holder of this Note as provided in the Note
Purchase Agreements referred to below.

         This Note is one of a series of Senior Notes, Series A (herein called
the "Notes"), issued pursuant to separate Note Purchase Agreements, each dated
as of February 14, 1997 (as from time to time amended, the "Note Purchase
Agreements"), between the Company and the respective Purchasers named therein
and is entitled to the benefits thereof. Each holder of this Note will be
deemed, by its acceptance hereof, (1) to have agreed to the confidentiality
provisions set forth in Section 20 of the Note Purchase Agreements and (2) to
have made the representation set forth in Section 6.2 of the Note Purchase
Agreements.

<PAGE>

                                    Exhibit 1
                              (to Fourth Amendment)

         As more fully provided in SECTION 2.2 of the Note Purchase Agreements,
the Company may issue and sell additional series of unsecured promissory notes
ranking pari passu with the Notes and, in connection therewith, may incorporate
by reference provisions of the Note Purchase Agreements or use the form of the
Note Purchase Agreements as the basis for the issuance of such additional notes.
Such incorporation by reference or use of the form of the Note Purchase
Agreements shall not dilute or otherwise affect the relative priority or other
rights of the holders of the Notes or in any way affect the percentages of the
Notes required to take action under the Note Purchase Agreements.

         This Note is a registered Note and, as provided in the Note Purchase
Agreements, upon surrender of this Note for registration of transfer, duly
endorsed, or accompanied by a written instrument of transfer duly executed, by
the registered holder hereof or such holder's attorney duly authorized in
writing, a new Note for a like principal amount will be issued to, and
registered in the name of, the transferee. Prior to due presentment for
registration of transfer, the Company may treat the person in whose name this
Note is registered as the owner hereof for the purpose of receiving payment and
for all other purposes, and the Company will not be affected by any notice to
the contrary.

         The Company will make required prepayments of principal on the dates
and in the amounts specified in the Note Purchase Agreements. This Note is also
subject to optional prepayment, in whole or from time to time in part, at the
times and on the terms specified in the Note Purchase Agreements, but not
otherwise.

         If an Event of Default, as defined in the Note Purchase Agreements,
occurs and is continuing, the principal of this Note may be declared or
otherwise become due and payable in the manner, at the price (including any
applicable Make-Whole Amount) and with the effect provided in the Note Purchase
Agreements.

         THIS NOTE SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE WITH, AND THE
RIGHTS AND PARTIES SHALL BE GOVERNED BY, THE LAW OF THE STATE OF ILLINOIS,
EXCLUDING CHOICE-OF-LAW PRINCIPLES OF THE LAW OF SUCH STATE WHICH WOULD REQUIRE
APPLICATION OF THE LAWS OF THE JURISDICTION OTHER THAN SUCH STATE.

                                          INSITUFORM TECHNOLOGIES, INC.

                                          By
                                            Name:_______________________________
                                            Title:______________________________

                                      -2-