Document:

<PAGE>

                                                                    EXHIBIT 10.1

                       FIRST AMENDMENT TO CREDIT AGREEMENT

      This FIRST AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is dated as of
March 16, 2005, between INSITUFORM TECHNOLOGIES, INC., a Delaware corporation
("Borrower"), and BANK OF AMERICA, N.A., a national banking association
("Lender").

      WHEREAS, the Borrower and the Lender are parties to that certain Amended
and Restated Credit Agreement dated as of March 12, 2004 (the "Original Credit
Agreement")(the Original Credit Agreement, as amended by this Amendment is
referred to herein as the "Credit Agreement");

      WHEREAS, the Borrower has requested that the Lender waive compliance with
certain provisions of the Original Credit Agreement, consent to certain
amendments to the Note Purchase Agreement-1997 and the Note Purchase
Agreement-2003, and consent to certain other transactions as more fully
described herein; and

      WHEREAS, the Lender is willing to accede to such requests in reliance upon
and in accordance with the terms, conditions, representations and warranties set
forth in this Amendment.

      NOW THEREFORE, in consideration of the mutual agreements herein and other
sufficient consideration, the receipt of which is hereby acknowledged, the
Borrower and the Lender hereby agree as follows:

      1.    DEFINITIONS. Unless otherwise specifically defined herein, each term
used herein which is defined in the Original Credit Agreement shall have the
meaning assigned to such term in the Original Credit Agreement. Each reference
to "hereof", "hereunder", "herein" and "hereby" and each other similar reference
and each reference to "this Agreement" and each other similar reference
contained in the Original Credit Agreement shall from the date hereof refer to
the Credit Agreement as amended hereby.

      2.    EFFECTIVENESS OF AGREEMENT. The effectiveness of this Amendment is
subject to the satisfaction and occurrence of the following conditions
precedent:

            (a)   The Lender shall have received the following documents in form
and substance satisfactory to the Lender:

                  (i)   Executed counterparts of this Amendment;

                  (ii)  Executed copies of a consent to this Amendment duly
      executed by each Guarantor party to the Master Guaranty;

                  (iii) The Fifth Amendment dated as of the date hereof to the
      Note Purchase Agreement-1997 (the "1997 NPA Amendment") and the Second
      Amendment dated as of the date hereof to the Note Purchase Agreement-2003
      (the "2003 NPA Amendment"), duly executed and delivered by the Borrower
      and the requisite noteholders thereunder needed to approve such amendments
      and such agreements shall be in form and substance satisfactory to the
      Lender;

                  (iv)  Copies of (a) the resolutions of the Borrower approving
      and authorizing the 1997 NPA Amendment and the 2003 NPA Amendment,
      certified by the Secretary or Assistant Secretary of the Borrower, and (b)
      any other certificates, documents, consents or

<PAGE>

      opinions delivered by any Borrower Party in connection with the 1997 NPA
      Amendment and the 2003 NPA Amendment; and

                  (v)   Such other assurances, certificates, documents, consents
      or opinions as the Lender reasonably may require.

            (b)   The Lender shall have received payment from Borrower of the
amendment fee set forth in that certain fee letter dated as of the date hereof
among the Borrower and the Lender.

            (c)   The Borrower shall have paid the fees, costs and expenses of
Bryan Cave LLP, special counsel to the Lender, incurred in connection with the
consummation of the transactions contemplated by this Amendment.

      3.    AMENDMENTS TO CREDIT AGREEMENT. Subject to the terms and conditions
set forth in Section 2 hereof, the Credit Agreement is hereby amended as
follows:

            (a)   The defined term "Maturity Date" in Section 1.01 of the Credit
      Agreement is amended by replacing the date "September 12, 2005" with
      "March 31, 2006".

            (b)   The defined term "Note Purchase Agreement-1997" in Section
      1.01 of the Credit Agreement is amended and restated in its entirety as
      follows:

            "Note Purchase Agreement-1997" means the Note Purchase Agreement
            dated as of February 14, 1997, as amended to and including March 15,
            2005, among Company and other parties signatory thereto under which
            Company issued certain 7.88% Senior Notes, Series A, due February
            14, 2007, of $110,000,000 aggregate principal amount; provided,
            however, that, except with respect to Section 8.01(f) of this
            Agreement (which is a cross default to other Indebtedness, including
            the Note Purchase Agreement-1997 as in effect from time to time),
            after March 15, 2005, no amendments to, or waivers of, the terms,
            conditions and definitions of the Note Purchase Agreement-1997
            referred to or incorporated by reference herein shall be deemed to
            amend or waive such terms, conditions and definitions for purposes
            of this Agreement unless Lender separately agrees or consents
            thereto hereunder. The terms, conditions and definitions referred to
            or incorporated by reference herein will survive termination,
            restatement or cancellation of the Note Purchase Agreement-1997 for
            purposes of this Agreement (other than Section 8.01(f)).

            (c)   The defined term "Note Purchase Agreement-2003" in Section
      1.01 of the Credit Agreement is amended and restated in its entirety as
      follows:

            "Note Purchase Agreement-2003" means the Note Purchase Agreement
            dated as of April 24, 2003, as amended to and including March 15,
            2005, among Company and other parties signatory thereto under which
            Company issued certain 5.29% Senior Notes, Series 2003-A, due April
            24, 2013, of $65,000,000 aggregate principal amount; provided,
            however, that, except with respect to Section 8.01(f) of this
            Agreement (which is a cross default to other Indebtedness, including
            the Note Purchase Agreement-2003 as in effect from time to time),
            after March 15, 2005, no amendments to, or waivers of, the terms,
            conditions and definitions of the Note Purchase Agreement-2003
            referred to or incorporated by reference herein shall be deemed to
            amend or waive such terms, conditions and

                                       2
<PAGE>

            definitions for purposes of this Agreement unless Lender separately
            agrees or consents thereto hereunder. The terms, conditions and
            definitions referred to or incorporated by reference herein will
            survive termination, restatement or cancellation of the Note
            Purchase Agreement-2003 for purposes of this Agreement (other than
            Section 8.01(f)).

            (d)   Section 1.01 of the Credit Agreement is amended by adding the
      following defined term:

            "Unrestricted Cash Balance" means as of any date of determination
            for the Borrower and its Subsidiaries on a consolidated basis, an
            amount equal to the sum of cash and cash equivalents (excluding any
            restricted cash balances or other retainage deposits), determined in
            accordance with GAAP.

            (e)   Section 2.03(j) of the Credit Agreement is amended by
      replacing the phrase "two and one-fourth percent (2.25%)" with the phrase
      "two and one-half percent (2.50%)".

            (f)   Section 2.08(a) of the Credit Agreement is amended by
      replacing the phrase "four-tenths of one percent (0.40%)" with the phrase
      "one-half of one percent (0.50%)".

            (g)   Section 7 of the Credit Agreement is amended by adding the
      following subsection at the end thereof:

            "7.05 MINIMUM CASH BALANCE. Permit, at any time, the Unrestricted
            Cash Balance to be less than $50,000,000 (or its equivalent in any
            other currency or currencies)."

            (h)   Exhibit B to the Credit Agreement is replaced in its entirety
      with Annex A attached hereto.

      4.    WAIVERS AND CONSENTS.

            (a)   Borrower has notified Lender that Borrower has violated
Section 10.2 (Fixed Charges Coverage Ratio) of the Note Purchase Agreement-1997
for the December 31, 2004 calculation date, which has given rise to an Event of
Default under Section 8.01(f) of the Credit Agreement (the "Covenant Default").
Borrower has requested that the Lender waive the Covenant Default, and the
Lender hereby waives the Covenant Default.

            (b)   Borrower has notified the Lender that Insituform Technologies
Limited, a foreign Subsidiary of the Borrower which is incorporated in England
and Wales ("ITL"), entered into a joint venture agreement with Environmental
Techniques Limited, a Northern Ireland company ("ETL") during calendar year
2004, pursuant to which ITL and ETL agreed to form Insituform Environmental
Techniques Limited, a Northern Ireland company ("IETL"), for the purpose of
promoting, marketing and distributing trenchless inspection, repair and
installation services in Northern Ireland and the Republic of Ireland. ITL has
entered into a subscription agreement for the purchase of 49.9% of the share
capital of IETL for (pound)499 (the "IETL Shares"). The Lender hereby waives
compliance with Section 7.01 of the Credit Agreement solely to the extent
necessary to waive any Default or Event of Default arising out of or relating to
the Borrower's subscription to purchase the IETL Shares, and the Lender hereby
consents to the purchase of

                                       3
<PAGE>

the IETL Shares by the Borrower pursuant to the subscription agreement provided
that the consideration for such purchase shall not exceed (pound)499.

            (c)   Subject to the terms and conditions set forth herein, the
Lender hereby consents to the execution and delivery by the Borrower of the 1997
NPA Amendment and the 2003 NPA Amendment.

            (d)   The waivers and consents contained in this Section 4 are
specific in intent and are valid only for the specific purpose for which given.
Nothing contained herein obligates the Lender to agree to any additional waivers
of or consents to any provisions of any of the Loan Documents. The waivers
contained in this Section 4 are waivers of those items set forth in subsections
(a) and (b) of this Section 4 only and shall not operate as a waiver of Lender's
right to exercise remedies resulting from (i) existing and/or continuing
Defaults or Events of Default of which Lender is not actually aware, or (ii)
other future Defaults or Events of Default, whether or not of a similar nature
and whether or not known to Lender.

      5.    NOTICE ADDRESS. The notice address of the Lender for purposes of
Section 10.02 of the Credit Agreement shall be as follows:

            Bank of America, N.A.
            MO1-800-12-01
            800 N. Market Street, 12th Floor
            St. Louis, MO 63101
            Attention: Jason R. Hickey
                       Senior Vice President
            Telephone: (314) 466-6811
            Facsimile: (314) 466-6499
            Email: jason.hickey@bankofamerica.com

                                       4
<PAGE>

            With a copy to:

            Harold R. Burroughs, Esq.
            Bart D. Wall, Esq.
            Bryan Cave LLP
            One Metropolitan Square, Suite 3600
            St. Louis, Missouri 63102-2750
            Telephone: (314) 259-2000
            Facsimile: (314) 259-2020
            Email: hrburroughs@bryancave.com
                   bdwall@bryancave.com

      6.    REPRESENTATIONS AND WARRANTIES OF BORROWER. Borrower hereby
represents and warrants to the Lender that (i) the Borrower's execution of this
Amendment has been duly authorized by all requisite action of the Borrower; (ii)
no consents are necessary from any third parties for the Borrower's execution,
delivery or performance of this Amendment, (iii) each of this Amendment, the
Credit Agreement and any other Loan Documents to which a Borrower Party is a
party constitute the legal, valid and binding obligations of such Borrower
Party, enforceable against such Borrower Party in accordance with its terms,
except to the extent that the enforceability thereof against such Borrower Party
may be limited by bankruptcy, insolvency or other laws affecting the
enforceability of creditors rights generally or by equity principles of general
application, (iv) the representations and warranties of the Borrower contained
in Section 5 of the Credit Agreement are true and correct in all material
respects on and as of the date hereof as if such representations and warranties
had been made on and as of the date hereof, except to the extent such
representations and warranties expressly relate to an earlier date, and (v)
after giving effect to this Amendment, there is no Default or Event of Default
under the Credit Agreement.

      7.    GOVERNING LAW. This Amendment shall be governed by, and construed in
accordance with, the law of the State of Missouri applicable to agreements made
and to be performed entirely within such state; provided that Lender shall
retain all rights arising under Federal law.

      8.    SECTION TITLES. The section titles in this Amendment are for
convenience of reference only and shall not be construed so as to modify any
provisions of this Amendment.

      9.    COUNTERPARTS; FACSIMILE TRANSMISSIONS. This Amendment may be
executed in one or more counterparts and on separate counterparts, each of which
shall be deemed an original, but all of which together shall constitute one and
the same instrument. Signatures to this Amendment may be given by facsimile or
other electronic transmission, and such signatures shall be fully binding on the
party sending the same.

      10.   STATUTORY NOTICE - ORAL COMMITMENTS. Nothing contained in the
following notice shall be deemed to limit or modify the terms of the Loan
Documents:

      ORAL AGREEMENTS OR COMMITMENTS TO LOAN MONEY, EXTEND CREDIT OR TO FORBEAR
      FROM ENFORCING REPAYMENT OF A DEBT INCLUDING PROMISES TO EXTEND OR RENEW
      SUCH DEBT ARE NOT ENFORCEABLE. TO PROTECT YOU (BORROWER) AND US (CREDITOR)
      FROM MISUNDERSTANDING OR DISAPPOINTMENT, ANY AGREEMENTS WE REACH COVERING
      SUCH MATTERS ARE CONTAINED IN THIS WRITING, WHICH IS THE COMPLETE AND
      EXCLUSIVE STATEMENT OF THE AGREEMENT BETWEEN US, EXCEPT AS WE MAY LATER
      AGREE IN WRITING TO MODIFY IT.

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<PAGE>

         11. POST-CLOSING ACTION. Notwithstanding anything to the contrary set
forth herein, the Borrower covenants and agrees to deliver to the Lender a copy
of the resolutions of the Board of Directors of Borrower, duly adopted, which
authorize and ratify the execution, delivery and performance of this Amendment
and the other documents executed pursuant to or in connection with this
Amendment, certified by the Secretary or Assistant Secretary of the Borrower.
Borrower agrees that the failure by Borrower to deliver such resolutions to
Lender on or before March 31, 2005 shall constitute an Event of Default under
the Credit Agreement and each of the other Loan Documents and the obligation of
the Lender to make additional Loans or issue Letters of Credit shall terminate
without any further action by the Lender.

            [The remainder of this page is intentionally left blank.]

                                       6
<PAGE>

      IN WITNESS WHEREOF, this Amendment has been duly executed as of the date
first above written.

                                    INSITUFORM TECHNOLOGIES, INC.

                                    By: /s/ Christian G. Farman
                                        --------------------------------------
                                        Christian G. Farman
                                        Senior Vice President, Chief Financial
                                        Officer and Assistant Secretary

                                    BANK OF AMERICA, N.A.

                                    By: /s/ Jason R. Hickey
                                        --------------------------------------
                                        Jason R. Hickey
                                        Senior Vice President<PAGE>

                                                                    EXHIBIT 10.2

Draft of March 15, 2005
================================================================================

                          INSITUFORM TECHNOLOGIES, INC.

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

                           FIFTH AMENDMENT AND WAIVER
                                       TO
                             NOTE PURCHASE AGREEMENT

                           Dated as of March 16, 2005

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

            Re: Note Purchase Agreement dated as of February 14, 1997
                                       and
                      $110,000,000 Senior Notes, Series A,
                              Due February 14, 2007

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

<PAGE>

                           FIFTH AMENDMENT AND WAIVER

                                       TO

                             NOTE PURCHASE AGREEMENT

      THIS FIFTH AMENDMENT AND WAIVER TO NOTE PURCHASE AGREEMENT dated as of
March 16, 2005 (the or this "Fifth Amendment") is between INSITUFORM
TECHNOLOGIES, INC., a Delaware corporation (the "Company"), and each of the
institutions holding a Note (as hereinafter defined) and party hereto
(collectively, the "Noteholders").

                                    RECITALS:

      A. The Company entered into the Note Purchase Agreement dated as of
February 14, 1997 (as amended, supplemented or otherwise modified through the
date hereof, the "Note Agreement"), pursuant to which the Company issued its
7.88% Senior Notes, Series A, due February 14, 2007 in the original aggregate
principal amount of $110,000,000 (as amended, supplemented or otherwise modified
through the date hereof, the "Notes").

      B. The Company and the Noteholders now desire to amend the Note Agreement
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. The Company has also advised the Noteholders that the Company has
violated certain terms and conditions set forth in the Note Agreement and more
particularly described herein and requests that the Noteholders waive such
Defaults and Events of Default.

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

      E. All requirements of law have been fully complied with and all other
acts and things necessary to make this Fifth 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 Fifth Amendment set forth in Section 4.1
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. WAIVER OF DEFAULTS.

      Section 1.1. Waiver of Defaults (Fixed Charge Coverage Ratio). The Company
has notified the Noteholders that the Company has violated the minimum Fixed
Charge Coverage Ratio required to be maintained under Section 10.2 of the Note
Agreement for the fiscal quarter ended December 31, 2004. The Noteholders hereby
waive the Event of Default arising under the Note Agreement on account of the
Company's violation of the financial covenant described above for the fiscal
quarter ended December 31, 2004.

<PAGE>

      Section 1.2. Waiver of Defaults and Consent (Acquisitions). The Company
has notified the Noteholders that Insituform Technologies Limited, a foreign
Subsidiary of the Company organized in England and Wales ("ITL"), entered into a
joint venture arrangement with Environmental Techniques Limited, a Northern
Ireland company ("ETL"), during the fiscal year ended 2004, pursuant to which
ITL and ETL formed a new company in Northern Ireland called Insituform
Environmental Techniques Limited ("IETL"), in connection with which ITL has
subscribed to purchase 499 shares of the authorized share capital (the
"Subscribed Joint Venture Shares") (comprised of a total of 1000 ordinary
shares) of IETL for an amount equal to (pound)499 (approximately equivalent to
U.S. $1,000). The Noteholders hereby waive compliance with Section 10.11 of the
Note Agreement to the extent necessary to waive any Event of Default arising
under the Note Agreement on account of the Subscribed Joint Venture Shares and
hereby consent to the purchase by ITL of the Subscribed Joint Venture Shares.

      Section 1.3. Limited Waivers; Reservation of Rights. The Company
acknowledges and agrees that the waivers granted in this Section 1 are specific
in intent and are valid only for the specific purpose for which they are being
given, are waivers the events described in Sections 1.1 and 1.2 hereof only,
shall not in any way obligate the Noteholders to agree to any additional waivers
of the provisions of the Note Agreement, including but not limited to Section
10.2, Section 10.11, Section 11(c) and Section 11(d) and shall not in any way be
deemed to constitute or operate as a waiver of any Noteholder's right under the
Note Agreement to exercise remedies resulting from (i) existing and/or
continuing Defaults or Events of Default of which such Noteholder is not
actually aware or (ii) other future Defaults or Events of Default, whether or
not of a similar nature and whether or not known to any Noteholder.

SECTION 2. AMENDMENTS TO NOTE AGREEMENT AND THE NOTES.

      Section 2.1. Amendment to Interest Rate on the Series A Notes. Upon the
Effective Date (as defined in Section 4.1 of this Fifth Amendment), the rate of
interest payable on each outstanding Note shall be changed from 8.63% per annum
to 8.88% per annum. As used in the Note Agreement and the Notes "Applicable
Rate" shall mean (i) 8.63% for the period commencing August 14, 2004 to but not
including the Effective Date and (ii) 8.88% from and after the Effective Date.

      Section 2.2. Amendment to Section 8.5 (Maturity; Surrender; etc.). Section
8.5 of the Note Agreement shall be and is hereby amended by deleting the
reference to "Section 8" therein and substituting in lieu thereof a reference to
"Section 8 or Section 10.7(b)".

      Section 2.3. Amendment to Section 9 (Additional Financial Covenants).
Section 9.9 of the Note Agreement shall be and is hereby amended in its entirety
to read as follows:

                  "Section 9.9. Additional Covenants. If the Bank Credit
            Agreement is amended, replaced or renewed after the Effective 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

                                      -2-
<PAGE>

            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. 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."

      Section 2.4. Amendment to Section 10.1 (Consolidated Net Worth). Section
10.1 of the Note Agreement shall be and is hereby amended in its entirety to
read as follows:

                  "Section 10.1. Consolidated Net Worth. The Company will not,
            at any time, permit Consolidated Net Worth to be less than the sum
            of (i) $260,000,000 plus (ii) 50% of Consolidated Net Income (if
            positive) on a cumulative basis for each fiscal quarter ending after
            December 31, 2004."

      Section 2.5. Amendment to Section 10.2 (Fixed Charge Coverage Ratio).
Section 10.2 of the Note Agreement shall be and is hereby amended in its
entirety to read as follows:

                  "Section 10.2. Fixed Charge Coverage Ratio. The Company will
            not at any time permit the Fixed Charge Coverage Ratio to be less
            than 1.25 to 1.0 for the fiscal quarters ending March 31, 2005 and
            June 30, 2005, 1.50 to 1.0 for the fiscal quarter ending September
            30, 2005, 1.75 to 1.0 for the fiscal quarter ending December 31,
            2005, 2.0 to 1.0 for each of the fiscal quarters ending March 31,
            2006 and June 30, 2006, 2.25 to 1.0 for each of the fiscal quarters
            ending September 30, 2006 and December 31, 2006, and 2.5 to 1.0 for
            each fiscal quarter ending thereafter."

      Section 2.6. Amendment to Section 10.3. (Limitation on Consolidated
Indebtedness). Section 10.3 of the Note Agreement shall be and is hereby amended
in its entirety to read as follows:

                                      -3-

<PAGE>

                  "Section 10.3. Limitation on Consolidated Indebtedness. The
            Company will not at any time permit (i) the Consolidated Leverage
            Ratio to exceed 4.25 to 1.0 for the fiscal quarter ending March 31,
            2005, 4.0 for the fiscal quarters ending June 30, 2005 and September
            30, 2005, and 3.0 to 1.0 for each fiscal quarter ending thereafter;
            and (ii) the ratio of Consolidated Total Indebtedness to
            Consolidated Total Capitalization to exceed 0.45 to 1.0; provided
            that in connection with any calculation of Indebtedness for purposes
            of determining compliance with this SECTION 10.3, there shall be
            excluded all Indebtedness of the Company and its Subsidiaries
            outstanding under any revolving credit agreement between the Company
            and a committed bank or banks if, during the 365-day period
            immediately preceding the date of any such calculation of
            Indebtedness, there shall have been a period of at least 60
            consecutive days on each day of which Indebtedness of the Company
            and its Subsidiaries outstanding under such revolving credit
            agreement is equal to zero by virtue, and solely by virtue, of such
            Indebtedness having been paid from general corporate funds of the
            Company and not from funds borrowed by the Company or any Subsidiary
            pursuant to any other revolving credit agreement for the purpose of
            paying such Indebtedness. If there shall not have been such 60
            consecutive day period on each day of which such Indebtedness was
            equal to zero, then and in such event there shall be included in
            such calculation of Indebtedness for purposes of this SECTION 10.3
            an amount equal to the average aggregate amount of all Indebtedness
            outstanding under such revolving credit agreement during such
            preceding 365-day period."

      Section 2.7. Amendment to Section 10.4 (Priority Debt). Section 10.4 of
the Note Agreement 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 $7,500,000 at any time. In addition
            from and after the Effective 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,

                                      -4-
<PAGE>

            at the time it becomes a Subsidiary, all Priority Debt of such
            Person existing immediately after it becomes a Subsidiary."

      Section 2.8. Amendment to Section 10.6 (Restricted Payments). Section 10.6
of the Note Agreement shall be and is hereby amended in its entirety to read as
follows:

                  "Section 10.6. Restricted Payments. 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) make any other payment or distribution, either directly or
            indirectly or through any Subsidiary, in respect of its capital
            stock."

      Section 2.9. Amendment to Section 10.7 (Mergers, Consolidations and Sales
of Assets).

      (a) Section 10.7(b)(iii)(1) of the Note Agreement shall be and is hereby
amended by deleting the reference to the phrase "25% of Consolidated Total
Assets, determined as set forth in the Company's most recently filed Form 10-K"
therein and substituting in lieu thereof a reference to "$20,000,000".

      (b) Section 10.7(b)(y)(C) of the Note Agreement shall be and is hereby
amended in its entirety to read as follows:

                  "(C) to prepay or retire Senior Indebtedness of the Company
            and/or its Subsidiaries; provided that the Company (i) shall offer
            to prepay each outstanding Note in a principal amount which equals
            the Ratable Portion for such Note, and (ii) any such prepayment of
            the Notes shall be made at par, together with accrued interest and
            the applicable Make-Whole Amount or other premium to the date of
            such prepayment, and".

      (c) The last paragraph of Section 10.7 of the Note Agreement shall be and
is hereby amended by the addition thereto of a new sentence at the end thereof
to read as follows:

            "If any holder of Senior Indebtedness elects not to accept such
            offer of prepayment, then, only for purposes of such application of
            an amount equal to such Net Proceeds for the prepayment of

                                      -5-
<PAGE>

            Senior Indebtedness, the Company nevertheless will be deemed on such
            particular occasion to have paid Senior Indebtedness in an amount
            equal to the Ratable Portion of such Senior Indebtedness."

      Section 2.9. Amendment to Section 10.9 (Prepayment and Purchase of Notes).
Section 10.10 of the Note Agreement shall be and is hereby amended in its
entirety to read as follows:

                  "Section 10.9. Prepayment and Purchase of Notes. Except as
            provided in SECTION 8.1 of this Agreement, so long as any 2003 Note
            shall be outstanding, 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 2.10. Amendment to Section 10.10 (Capital Expenditures and
Acquisitions). Section 10.10 of the Note Agreement shall be and is hereby
amended in its entirety to read as follows:

                  "Section 10.10. Capital Expenditures and Acquisitions. The
            Company will not, and will not permit any Subsidiary to, make any
            (a) Capital Expenditures or (b) acquisitions of stock or other
            equity interests in any Person, or all or substantially all of the
            assets of any Person if the aggregate amount of all such Capital
            Expenditures and acquisitions made by the Company and its
            Subsidiaries would exceed (i) $40,000,000 during the fiscal year
            ending December 31, 2005 and (ii) $40,000,000 during the fiscal year
            ending December 31, 2006; provided that any calculation of Capital
            Expenditures during such periods shall be done net of proceeds
            realized by the Company from the routine sale of fixed assets in the
            ordinary course of business during such period so long as such sale
            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)(y)(A) and (B)."

      Section 2.11. Amendment to Section 10.11 (Deletion of Acquisition; New
Covenant). Section 10.11 of the Note Agreement shall be and is hereby amended in
its entirety to read as follows:

                  "Section 10.11. Bank Credit Agreement.

                  (a) The Company shall at all times maintain a Bank Credit
            Agreement which provides for commitments in favor of the Company of
            not less than $25,000,000.

                                      -6-
<PAGE>

                  (b) So long as the Company is required to maintain an
            Unrestricted Cash Balance under the Bank Credit Agreement, initially
            $50,000,000 or its equivalent in any other currency, the Company
            will not permit such Unrestricted Cash Balance to be less than the
            amount from time to time required under the Bank Credit Agreement."

      Section 2.12. Amendment to Section 11 (Events of Default). Section 11(c)
of the Note Agreement shall be and is hereby amended in its entirety to read as
follows:

                  "(c) the Company defaults in the performance of or compliance
            with the terms of SECTION 7.1(d), SECTION 9.8 or any term contained
            in SECTION 10; or".

      Section 2.13. Amendment to Section 11 (Events of Default). Section 11(f)
of the Note Agreement shall be and is hereby amended by deleting the reference
to "from and after the Effective Date to and including the Transition Date," in
clause (ii) thereof.

      Section 2.14. Amendment to Schedule B (Definitions - Amended Terms). The
definitions of "Applicable Rate", "Capital Expenditures", "Default Rate",
"Effective Date" and "Interest Expense" shall be and are hereby amended in their
entirety to read as follows:

                  "`Applicable Rate' has the meaning set forth in Section 2.1 of
            the Fifth 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 but only to the extent to which the Company
            has received payments under the contract sufficient to cover the
            cost of the equipment."

                  "Default Rate' means that rate of interest that is the greater
            of (i) 10.88% per annum or (ii) 2% over the rate of interest
            publicly announced by JP Morgan Chase Bank in New York, New York as
            its base or "prime" rate."

                  "Effective Date' has the meaning set forth in Section 4.1 of
            the Fifth Amendment."

                  "`Effective Date' has the meaning set forth in Section 4.1 of
            the Fifth Amendment."

                  "`Interest Expense' means, with respect to any period, the sum
            (without duplication) of the following (in each case, after
            eliminating all offsetting debits and credits between the Company
            and its Subsidiaries and all other items required to be eliminated
            in

                                      -7-
<PAGE>

            the course of the preparation of the consolidated financial
            statements of the Company and its Subsidiaries in accordance with
            GAAP): (a) all interest in respect of Indebtedness of the Company
            and its Subsidiaries (including imputed interest on Capitalized
            Rentals) deducted in determining Consolidated Net Income for such
            period, and (b) all debt discount and expense amortized or required
            to be amortized in the determination of Consolidated Net Income for
            such period."

      Section 2.14. Amendment to Schedule B (Definitions - New Terms). Schedule
B of the Note Agreement shall be and 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:

                  "`Bank Credit Agreement' shall mean the Amended and Restated
            Credit Agreement dated as of March 12, 2004 between the Company and
            Bank of America, N.A., as such agreement may be amended, restated,
            joined, supplemented, renewed, replaced, refunded or refinanced from
            time to time and any successor bank credit facility which
            constitutes the primary bank credit facility of the Company."

                  "`Consolidated Income Available for Fixed Charges' shall mean,
            with respect to any period, the sum of (i) EBITDA for such period
            and (ii) Rentals for such period."

                  "`Consolidated Leverage Ratio' shall mean, on any date, the
            ratio of Consolidated Total Indebtedness at such date to EBITDA for
            the period of the four consecutive fiscal quarters most recently
            ended as of such date. For purposes of calculating EBITDA for any
            period of four consecutive fiscal quarters, if during such period
            the Company or any Subsidiary shall have acquired any Person which
            becomes a Subsidiary or acquired all or substantially all of the
            operating assets of any Person or disposed of any Subsidiary or all
            or substantially all of the operating assets of any Subsidiary or
            disposed of any segment of the business of the Company or a
            Subsidiary, EBITDA for such period shall be calculated after giving
            pro forma effect thereto as if such acquisition or disposition
            occurred on the first day of such period of four consecutive fiscal
            quarters."

                  "`Consolidated Net Income' shall mean, for any period, the net
            income (or loss), before any extraordinary items, of the Company and
            its Subsidiaries for such period (taken as a cumulative whole), as
            calculated in accordance with GAAP."

                                      -8-
<PAGE>

                  "`Consolidated Net Worth' shall mean, as of any date of
            determination thereof, the consolidated stockholder's equity of the
            Company and its Subsidiaries, as determined in accordance with
            GAAP."

                  "`EBITDA' shall mean, with respect to any period, the total of
            the following calculated without duplication for the Company and its
            Subsidiaries on a consolidated basis for such period: (a)
            Consolidated Net Income for such period; plus (b) taxes deducted in
            determining Consolidated Net Income for such period; plus (c)
            Interest Expense deducted in determining Consolidated Net Income for
            such period; plus (d) amortization and depreciation expense deducted
            in determining Consolidated Net Income for such period."

                  "`Fair Market Value' means, at any time and with respect to
            any property, the sale value of such property that would be realized
            in an arm's-length sale at such time between an informed and willing
            buyer and an informed and willing seller (neither being under a
            compulsion to buy or sell), as reasonably determined in the good
            faith opinion of the Company's board of directors."

                  "`Fifth Amendment' means the Fifth Amendment and waive to Note
            Purchase Agreement dated as of March 16, 2005 between the Company
            and the holders of Notes, in respect of this Agreement."

                  "`Fixed Charge Coverage Ratio' means, on any date, the ratio
            of (a) Consolidated Income Available for Fixed Charges for the
            period of four consecutive fiscal quarters ending on, or most
            recently ended prior to, such date to (b) Consolidated Fixed Charges
            for such period."

                  "`Net Proceeds' means with respect to any sale of property by
            any Person an amount equal to (a) the aggregate amount of the
            consideration received by such Person in respect of such sale
            (valued at the Fair Market Value of such consideration at the time
            of such sale), minus (b) the sum of (i) all out-of-pocket costs and
            expenses actually incurred by such Person in connection with such
            sale, and (ii) all state, federal and foreign taxes incurred, or to
            be incurred, by the seller in connection with such sale."

                  "`Ratable Portion' means, with respect to any Note, an amount
            equal to the product of (x) the amount equal to the Net Proceeds
            being so applied to the prepayment of Senior Indebtedness multiplied
            by (y) a fraction the numerator of which is the outstanding
            principal amount of such Note and the

                                      -9-
<PAGE>

            denominator of which is the aggregate principal amount of Senior
            Indebtedness of the Company and its Subsidiaries."

                  "`Unrestricted Cash Balance' means as of any date of
            determination for the Company and its Subsidiaries on a consolidated
            basis, an amount equal to the sum of cash and cash equivalents
            (excluding any restricted cash balances or other retainage
            deposits), determined in accordance with GAAP."

      Section 2.15. Amendment to Schedule B (Definitions - Deletions). The
definition of "Consolidated Cash Flow Available for Fixed Charges" shall be and
is hereby deleted from Schedule B to the Note Agreement.

SECTION 3. REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

      Section 3.1. To induce the Noteholders to execute and deliver this Fifth
Amendment, the Company represents and warrants (which representations shall
survive the execution and delivery of this Fifth Amendment) to the Noteholders
that:

                  (a) this Fifth Amendment has been duly authorized, executed
            and delivered by it and this Fifth 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 Agreement and the Notes, as amended by this Fifth
            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 Fifth 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 3.1(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;

                                      -10-
<PAGE>

                  (d) as of the date hereof and after giving effect to this
            Fifth 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, 2004 furnished to you do not, nor
            does any written statement furnished by the Company to you in
            connection with the execution and delivery of this Fifth Amendment,
            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 Fifth Amendment, except for the legal fees of
            counsel to the holders of such indebtedness and consideration paid
            to the holders of the 2003 Notes which is identical to the
            consideration to be paid to the holders of the Notes and
            consideration paid to Bank of America, N.A. pursuant to and as set
            forth in the First Amendment to Credit Agreement dated as of March
            16, 2005 (the "Bank Credit Agreement Amendment") between the Company
            and Bank of America, N.A. (in respect of the Amended and Restated
            Credit Agreement dated as of March 12, 2004 (the "Bank Credit
            Agreement") between the Company and Bank of America, N.A.).

SECTION 4. CONDITIONS TO EFFECTIVENESS OF THIS FIFTH AMENDMENT.

      Section 4.1. This Fifth Amendment shall become effective when each of the
following conditions has been satisfied:

                  (a) executed counterparts of this Fifth 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 3 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 Second Amendment to Note Purchase Agreement dated as
            of March 16, 2005, in respect of the 2003 Notes, shall have been
            duly executed and delivered by the requisite percentage of the
            noteholders thereunder needed to approve such amendment and such
            agreement shall be in form and substance satisfactory to each
            Noteholder;

                                      -11-
<PAGE>

                  (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
            Fifth Amendment, in form and substance reasonably satisfactory to
            the Noteholders and their special counsel to the effect that this
            Fifth Amendment constitutes the legal, valid and binding obligation
            of the Company;

                  (g) the Bank Credit Agreement Amendment shall have been duly
            executed and delivered by the parties thereto and such agreement
            shall be in form and substance satisfactory to each Noteholder
            executing this Fifth Amendment; and

                  (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 Fifth Amendment.

Upon receipt of all of the foregoing, this Fifth Amendment shall become
effective. Delivery of this Fifth 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 Fifth 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 2.1 hereof shall begin to accrue.

SECTION 5. MISCELLANEOUS.

      Section 5.1. 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
2.1 of this Fifth 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 5.2. Release of Claims. In further consideration of each
Noteholder's execution of this Fifth Amendment, the Company hereby releases each
Noteholder and its respective affiliates, officers, employees, directors,
trustees, agents and attorneys (collectively, the "Releasees") from any and all
claims, demands, liabilities, responsibilities, disputes, causes of action
(whether at law or in equity) and obligations of every nature whatsoever,
whether liquidated or unliquidated, known or unknown, matured or unmatured,
fixed or contingent, that the Company may have against the Releasees which arise
from or relate to any actions which the Releasees may have taken or omitted to
take prior to the date thereof with respect to the Notes, the Note Agreement or
any Subsidiary Guaranty. For purposes of the release contained in this

                                      -12-
<PAGE>

section, the term "Company" shall mean and include such party's successors and
assigns, including, without limitation, any trustees acting on behalf of such
party and any debtor-in-possession in respect of such party.

      Section 5.3. The Company acknowledges and agrees that by agreeing to the
amendments of the Note Agreement 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 Agreement, which
rights are hereby expressly reserved by the holders of the Notes.

      Section 5.4. This Fifth Amendment shall be construed in connection with
and as part of the Note Agreement, and except as modified and expressly amended
by this Fifth Amendment, all terms, conditions and covenants contained in the
Note Agreement and the Notes are hereby ratified and shall be and remain in full
force and effect.

      Section 5.5. Any and all notices, requests, certificates and other
instruments executed and delivered after the execution and delivery of this
Fifth Amendment may refer to the Note Agreement without making specific
reference to this Fifth Amendment but nevertheless all such references shall
include this Fifth Amendment unless the context otherwise requires.

      Section 5.6. The descriptive headings of the various Sections or parts of
this Fifth Amendment are for convenience only and shall not affect the meaning
or construction of any of the provisions hereof.

      Section 5.7. This Fifth Amendment shall be governed by and construed in
accordance with Illinois law.

                                      -13-
<PAGE>
     The execution hereof by you shall constitute a contract between us for the
uses and purposes hereinabove set forth, and this Fifth 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
                                         Name:   Christian G. Farman
                                         Title:  Senior Vice President and CFO

<PAGE>

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

                                      THE NORTHWESTERN MUTUAL LIFE INSURANCE
                                        COMPANY

                                      By /s/ David A. Barras
                                         Name:  David A. Barras
                                         Title: Authorized Representative

<PAGE>

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

                                      PRINCIPAL LIFE INSURANCE COMPANY

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

                                           By /s/ Jon C. Heing
                                              ----------------------------------
                                              Name: Jon C. Heing
                                                   -----------------------------
                                              Title: Counsel
                                                     ---------------------------

                                           By /s/ Stephen G. Skrivanek
                                              ----------------------------------
                                              Name: Stephen G. Skrivanek
                                                   -----------------------------
                                              Title: Counsel
                                                     ---------------------------

<PAGE>

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

                                      ALLSTATE LIFE INSURANCE COMPANY

                                      By _______________________________________

                                      By _______________________________________
                                         Authorized Signatories

<PAGE>

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

                                      CONNECTICUT GENERAL LIFE INSURANCE COMPANY

                                      By:  CIGNA Investments, Inc. (authorized
                                           agent)

                                           By /s/ Stephen A. Osborn
                                              Name:  Stephen A. Osborn
                                              Title:    Managing Director

                                      LIFE INSURANCE COMPANY OF NORTH AMERICA

                                      By:  CIGNA Investments, Inc. (authorized
                                           agent)

                                           By /s/ Stephen A. Osborn
                                              Name:  Stephen A. Osborn
                                              Title:    Managing Director

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

                                      By:  CIGNA Investments, Inc. (authorized
                                           agent)

                                           By /s/ Stephen A. Osborn
                                              Name:  Stephen A. Osborn
                                              Title:    Managing Director

<PAGE>

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

                                      JEFFERSON-PILOT LIFE INSURANCE COMPANY

                                      By _______________________________________
                                         Its____________________________________

                                      JEFFERSON PILOT FINANCIAL INSURANCE
                                        COMPANY

                                      By
                                         Its____________________________________

<PAGE>

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

                                      RELIASTAR LIFE INSURANCE COMPANY
                                      RELIASTAR LIFE INSURANCE COMPANY
                                                 OF NEW YORK

                                      By:  ING Investment Management LLC,
                                           as Agent

                                           By /s/ James Wittich
                                              Name:  James Wittich
                                              Title: Senior Vice President

<PAGE>

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

                                      ACE PROPERTY & CASUALTY INSURANCE COMPANY

                                      By:   Columbia Management Advisors
                                            Incorporated, as agent

                                            By /s/ Richard A. Hegwood
                                                Name:  Richard A. Hegwood
                                                Title: Senior Vice President

<PAGE>

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

                                      THE SECURITY FINANCIAL LIFE INSURANCE CO.

                                      By /s/ David T. Wallman
                                         Name:  David T. Wallman
                                         Title: Senior Vice President & Chief
                                                Actuary

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