<PAGE>

                                                                   EXHIBIT 10.56


                                   SUBLEASE

     THIS SUBLEASE AGREEMENT ("Sublease"), made and entered on the 22nd day
December 1999, by and between WILLIAMS COMMUNICATIONS, INC., a Delaware
corporation formerly known as CRITICAL TECHNOLOGIES, INC., a Missouri
corporation ("Sub-Landlord") and CONCENTRIC NETWORK CORPORATION, a Delaware
corporation ("Sub-Tenant") (collectively the "parties").

                                  WITNESSETH:

     WHEREAS, an office building lease with an effective date of February 26,
1997, was entered into by and between Sub-Landlord as Tenant and Armstrong
Properties, LTC as Landlord (the "Lease");

     WHEREAS, the Premises covered by the Lease is an approximately 23,500
square foot office building and adjoining parking areas located at 944 Anglum
Drive, Hazelwood, Missouri 63042 (the "Premises"). Sub-Landlord desires to
sublet the entire Premises (hereinafter the "Sublease Premises") to Sub-Tenant,
and Sub-Tenant desires to Rent from Sub-Landlord the Sublease Premises.

     WHEREAS, the parties have reached an agreement by which Sub-Tenant would
sublease the Sublease Premises from Sub-Landlord; and

     WHEREAS, the parties desire to set forth the terms and conditions of the
sublease of the Sublease Premises.

     NOW, THEREFORE, in consideration of the premises and the following mutual
covenants, the parties hereby agree:

1.   Recitals: The above recitals are incorporated herein as terms of this
     Sublease.

2.   Sublease: Sub-Landlord hereby subleases to Sub-Tenant and Sub-Tenant hereby
     subleases from Sub-Landlord the Sublease Premises, subject to and
     conditioned upon obtaining the consent of Landlord to this Sublease.

3.   Lease: Sub-Tenant represents and warrants that it has received a conformed
     copy of the Lease, that it has reviewed the same, and that it agrees to
     comply with the terms thereof the same as if it were the Tenant
<PAGE>

     thereunder, except as otherwise provided herein. This Sublease is and shall
     remain subordinate to the terms and conditions of the Lease. To the extent
     that Sub-Landlord has rights or obligations under the Lease as Tenant, Sub-
     Tenant has the same rights or obligations with respect to the Sublease
     Premises. This Sublease shall not increase any obligation of Sub-Landlord
     beyond its obligations as a Tenant under the Lease. A copy of the Lease is
     attached hereto as Exhibit "A" and made a part hereof by reference.

4.   Term: The Sublease shall commence on November 1, 1999, (the "Commencement
     Date") subject to Landlord's consent to the Sublease, and terminate on
     March 31, 2002 (the "Termination Date"), unless sooner terminated as
     hereinafter provided (the "Sublease Term"). If Landlord's consent has not
     occurred for any reason whatsoever on or before December 15, 1999, then
     either party may terminate the Sublease by written notice to the other and
     Sub-Tenant shall promptly vacate the Sublease Premises.

5.   Basic Rent: Sub-Tenant shall pay Sub-Landlord as Rent for the Sublease
     Premises the sum Fourteen Thousand Six Hundred Eighty Seven and 00/100
     Dollars ($14,687.00) per month from November 1, 1999, through March 31,
     2000; and, commencing April 1, 2000, through March 31, 2002, Sub-Tenant
     shall pay Sub-Landlord as Rent for the Sublease Premises the sum Sixteen
     Thousand Six Hundred Forty Five and 00/100 Dollars ($16,645.00) per month.
     Rent shall be payable in advance without demand on the first day of each
     and every month during the remaining term of the Lease. Any Rent accrued
     prior to obtaining Landlord's consent to the Sublease shall be due and
     payable on obtaining Landlord's consent. A late charge of five percent (5%)
     of any monthly payment will be added after fifteen (15) days from the due
     date and paid by Sub-Tenant. Sub-Tenant's failure to pay any monthly rental
     within ten (10) days after the due date shall be deemed an event of default
     under this Sublease.

6.   Operating Expenses: Sub-Tenant shall, from the Commencement Date, pay Sub-
     Landlord for all gas, electricity, water, air conditioning, sewer and
     telephone service and all other utilities used in and upon the Sublease
     Premises. Sub-Tenant shall pay for its own trash removal.
<PAGE>

7.   Real Estate Taxes: Sub-Tenant shall pay all real estate and occupancy
     taxes, assessments, and/or installments thereon (collectively, "Taxes") on
     or before the date the same shall become due, whether general or special,
     foreseen and unforeseen, and shall furnish Landlord and Sub-Landlord a copy
     of the paid receipts therefor. Taxes shall be pro-rated between Sub-
     Landlord and Sub-Tenant for the year 1999, according to the Commencement
     Date.

8.   Use of Sublease Premises:

     8.1  The Sublease Premises are subleased to Sub-Tenant in "as is" condition
          with all faults as of the Commencement Date of the Sublease Term and
          Sub-Landlord has made no representation or warranty, express or
          implied, with respect to the condition of the Sublease Premises, or
          appurtenant grounds or facilities or with respect to their suitability
          for the conduct of Sub-Tenant's business or other intended use. Prior
          to the Commencement Date, Sub-Landlord shall have cleared all debris
          from the Sublease Premises and shall deliver the Sublease Premises to
          Sub-Tenant in vacant, good, "broom-clean" condition, with all systems
          that were Tenant's responsibility under the Lease in good working
          order. Sub-Tenant's acceptance of the Sublease Premises shall not be
          deemed a waiver of the above representations. Subject to Landlord's
          consent, Sub-Landlord hereby approves Sub-Tenant's installation of the
          alterations described in Exhibit "B", attached hereto, and subject to
          Landlord's consent agrees the Sub-Tenant may surrender such
          alterations on the termination of the Sublease.

     8.2  The Sublease Premises are to be used only for the purposes allowed by
          the Lease, including a data center, and must be continuously occupied
          by Sub-Tenant.

     8.3  Upon the termination of the Sublease, Sub-Tenant will return the
          Sublease Premises to Sub-Landlord in the same condition as the
          Sublease Premises were in as of the Commencement Date of this
          Sublease,
<PAGE>

          reasonable wear and tear, casualty and condemnation damage, and
          approved alterations excepted.

9.   Assignment and Subletting: Sub-Tenant will not assign this Sublease or
     sublet the Sublease Premises without the prior written consent of Landlord
     and Sub-Landlord. Sub-Landlord shall not unreasonably withhold or delay its
     consent. Provided, Sub-Tenant may, without Sub-Landlord's prior written
     consent (but subject to Landlord's consent to the extent required under the
     Lease), sublet the Sublease Premises or assign the Sublease to (i) an
     entity controlling, controlled by or under common control with Sub-Tenant;
     (ii) a successor entity related to Sub-Tenant by merger, consolidation,
     nonbankruptcy reorganization, or government action; or (iii) a purchaser of
     substantially all of Sub-Tenant's assets located in the Sublease Premises.
     In the event of any sublease or assignment pursuant to (i), (ii), or (iii)
     above, Sub-Tenant shall remain liable under this Sublease.    A transfer of
     Sub-Tenant's capital stock shall not be deemed an assignment, subletting or
     any other transfer of the Sublease or the Sublease Premises.

10.  No Real Estate Broker: Each of the parties represents that no real estate
     broker was used in connection with this Sublease.

11.  No Security Deposit: Sub-Tenant acknowledges that Sub-Landlord has
     deposited with Landlord the sum Sixteen Thousand Six Hundred Forty Five and
     00/100 Dollars ($16,645.00) as a Security Deposit pursuant to paragraph 6
     of the Lease, and agrees to make no claim to or against said Security
     Deposit or any portion thereof on termination of this Sublease, or
     otherwise. Sub-Landlord will not require any security deposit from Sub-
     Tenant under this Sublease.

12.  No Option to Renew: Sub-Tenant may not exercise the Option to Renew granted
     to Sub-Landlord under paragraph 31 of the Lease unless Landlord shall first
     have agreed in writing with Sub-Landlord and Sub-Tenant that Sub-Landlord
     shall have no further liability under the Lease or Sublease whatsoever with
     respect to the extension period, and that Sub-Landlord shall receive full
     refund of the Security Deposit on termination of the Lease. Sub-Landlord
     shall not exercise the Option to Renew
<PAGE>

     unless first obtaining Sub-Tenant's prior written consent.

13.  Notice and Payment Addresses: Notices shall be delivered in the manner set
     forth in Section 22 of the Lease to the addresses set forth below:

     Sub-Landlord:

          Williams Communications, Inc.
          One Williams Center
          Suite 2200
          Tulsa, Oklahoma 74172
          Attn: Director of Facilities Management

     Sub-Tenant:

          Concentric Network Corporation
          944 Anglum Drive
          Hazelwood, Missouri 63042
          Attn: Office Manager

          Concentric Network Corporation
          10590 North Tantau Avenue
          Cupertino, California 95014
          Attn: Director of Administration

     Landlord:

          Armstrong Properties, LTC
          31 Fordyce
          St. Louis, MO 63124
          Attn: Mr. William H. Armstrong

14.  Termination of Lease: The parties hereto agree that in the event the Lease
     terminates, then this Sublease shall also terminate on that same date.

15.  Insurance: Sub-Tenant agrees, at its sole cost and expense, during the term
     of this Sublease to maintain in full force and effect insurance coverages
     in form and substance as required of Tenant under the Lease, and to name
     Sub-Landlord as an additional insured in each case in which Landlord must
     be named an additional insured as provided by the Lease.

16.  Sub-Landlord Warranties:
<PAGE>

     16.1  Sub-Landlord represents and warrants the following to Sub-Tenant:

          16.1.1 The Lease is in full force and effect and that there is no
          default thereunder or to Sub-Landlord's knowledge no event which, with
          the passage of time and giving of notice or both, would constitute a
          default thereunder.

          16.1.2 Sub-Landlord has corporate authority to enter into this
          Sublease and perform its obligations hereunder.

          16.1.3 This Sublease evidences a valid and binding contractual
          obligation of Sub-Landlord enforceable in accordance with its terms.

          16.1.4 The copy of the Lease attached hereto as Exhibit A is a true,
          correct and complete copy of the Lease.

17.  Sub-Tenant's Authority:

     17.1  Sub-Tenant represents and warrants the following to Sub-Landlord:

          17.1.1  Sub-Tenant has corporate authority to enter into this Sublease
          and perform its obligations hereunder.

          17.1.2  This Sublease evidences a valid and binding contractual
          obligation of Sub-Tenant.

18.  Indemnification: The following indemnification provisions shall apply.

          (a) By Sub-Landlord. Sub-Landlord will indemnify, defend, protect, and
              ---------------
          hold Sub-Tenant, its officers, directors, employees, and agents
          (collectively, the "Sub-Tenant Indemnitees") harmless from and against
          any and all demands, actions or causes of action, assessments,
          judgments, damages, obligations, liabilities and claims (collectively,
          "Claims") of every type and nature whatsoever (including, without
          limitation, injury to or death of any person or persons, or
<PAGE>

          damage to or loss of any property) and shall reimburse the Sub-Tenant
          Indemnitees for any and all financial expenditures, costs and expenses
          (including, without limitation, interest, penalties and reasonable
          attorneys' fees, reasonable consultants' fees, expenses and court
          costs incurred in connection therewith and all reasonable costs and
          expenses of investigating and defending any claim or any order,
          directive, final judgment, compromise, settlement, fine, penalty,
          court costs or proceeding) in consequence of such Claims arising from
          or related to:

               (i)   any inaccuracy in or breach by Sub-Landlord of any
               representation or warranty made by it herein; or

               (ii)  any claim or demand for commission or other compensation by
               any broker, finder, agent or similar intermediary claiming to
               have been employed by or on behalf of Sub-Landlord, in connection
               with this transaction; or

               (iii) any contamination at, on, in, above or beneath the Sublease
               Premises during the term of the Lease and preceding the term of
               the Sublease; or

               (iv)  any negligent acts or omissions, or willful misconduct, by
               Sub-Landlord, its employees or agents, which result in or cause
               harm or damage to any person or property, in, upon, or about the
               Sublease Premises; or

               (v)   any event of default by Sub-Landlord under the Lease or
               this Sublease.

          (b)  By Sub-Tenant. Sub-Tenant will indemnify, defend, protect, and
               -------------
          hold Sub-Landlord and Landlord and any affiliated company thereto,
          their respective officers, directors, stockholders, managers, members,
          employees, and agents (the "Sub-Landlord Indemnitees") harmless from
          and against any and all demands, actions or
<PAGE>

          causes of action, assessments, judgments, damages, obligations,
          liabilities and claims (collectively, "Claims") of every type and
          nature whatsoever (including, without limitation, injury to or death
          of any person or persons, or damage to or loss of any property) and
          shall reimburse the Sub-Landlord Indemnitees for any and all financial
          expenditures, costs and expenses (including, without limitation,
          interest, penalties and reasonable attorneys' fees, reasonable
          consultants' fees, expenses and court costs incurred in connection
          therewith and all reasonable costs and expenses of investigating and
          defending any claim or any order, directive, final judgment,
          compromise, settlement, fine, penalty, court costs or proceeding) in
          consequence of such Claims, and arising from or pursuant to:

               (i)   any inaccuracy in or breach by Sub-Tenant of any
               representation or warranty made by it herein;

               (ii)  any claim or demand for commission or other compensation by
               any broker, finder, agent or similar intermediary claiming to
               have been employed by or on behalf of Sub-Tenant in connection
               with this transaction;

               (iii) any contamination at, on, in, above or beneath the Sublease
               Premises during the term of this Sublease caused or created by
               Sub-Tenant or its agents, employees, or contractors; or

               (iv)  any negligent acts or omissions, or willful misconduct, by
               Sub-Tenant, its employees or agents, which result in or cause
               harm or damage to any person or property, in, upon, or about the
               Sublease Premises; or

               (v)   any event of default by Sub-Tenant under this Sublease.

19.  Applicable Law: This Sublease shall be construed according to the laws of
     the State of Missouri.
<PAGE>

20.  Headings: The headings in this Sublease are for reference only and do not
     expand or limit the terms agreed to by the parties.

21.  Entire Agreement: This Sublease represents the entire agreement between the
     parties and no modification hereof shall be effective unless first reduced
     to writing and signed by both parties.

22.  Incorporation of Lease. All of the provisions of the Lease are incorporated
     herein as if set forth in their entirety herein, except (a) the following
     provisions shall not be incorporated herein: Sections 4 (the first sentence
     only), 5, 6, 22, 31, and 32; and (b) references to "Landlord" in the
     following provisions shall mean "Landlord" only: Sections 10 (except the
     fourth paragraph), 11 (except the first sentence), 14, 17 (the third
     through seventh sentences only) and 19 (except the last sentence of subpart
     (a)). References in the Lease as incorporated herein to "Landlord",
     "Tenant", "Lease" and "Leased Premises" shall be deemed to refer to "Sub-
     Landlord", "Sub-Tenant", "Sublease" and "Sublease Premises", respectively;
     provided, however, that (i) with respect to work, services, repairs,
     restoration, insurance or any other similar obligation of Landlord under
     the Lease, the sole obligation of Sub-Landlord shall be to use Sub-
     Landlord's reasonable efforts to obtain Landlord's performance as set forth
     below; and (ii) with respect to any consent or approval required to be
     obtained from the "Landlord" under the Lease, such consent must be obtained
     from both Landlord and Sub-Landlord, and the approval of Sub-Landlord may
     be withheld if Landlord's consent is not obtained.

23.  Quiet Enjoyment. In the event that Sub-Landlord defaults in the performance
     or observance of any of Sub-Landlord's remaining obligations under the
     Lease or fails to perform Sub-Landlord's stated obligations under the
     Sublease, then Sub-Tenant shall give Sub-Landlord notice specifying in what
     manner Sub-Landlord has defaulted, and if such default shall not be cured
     by Sub-Landlord within thirty (30) days thereafter (except that if such
     default cannot be cured within said thirty (30) day period, this period
     shall be extended for an additional reasonable time, provided
<PAGE>

     that Sub-Landlord commences to cure such default within such thirty (30)
     day period and proceeds diligently thereafter to effect such cure as
     quickly as possible), then Sub-Tenant shall be entitled to cure such
     default and promptly collect from Sub-Landlord Sub-Tenant's reasonable
     expenses in so doing (including, without limitation, reasonable attorneys'
     fees). Sub-Tenant shall not be required, however, to wait the entire cure
     period described herein if earlier action is required to comply with the
     Lease or with any applicable governmental law, regulation or order.

24.  Sub-Landlord's Obligations. Sub-Landlord shall fully perform all of its
     obligations under the Lease to the extent Sub-Tenant has not agreed to
     perform such obligations under the Sublease. Sub-Landlord shall not
     terminate or take any action under the Lease that could give rise to the
     termination of the Lease, amend or waive any provisions under the Lease or
     make any elections, exercise any right or remedy or give any consent or
     approval under the Lease without, in each instance, Sub-Tenant's prior
     written consent if any of the foregoing would materially adversely affect
     Sub-Tenant's rights or obligations hereunder. Sub-Landlord, with respect to
     the obligations of Landlord under the Lease, shall use Sub-Landlord's
     diligent good faith efforts to cause Landlord to perform such obligations
     for the benefit of Sub-Tenant. Such diligent good faith efforts shall
     include, without limitation: (a) upon Sub-Tenant's written request,
     immediately notifying Landlord of its nonperformance under the Lease, and
     requesting that Landlord perform its obligations under the Lease; and (b)
     to commence litigation against Landlord to obtain the performance required
     from Landlord under the Lease.

25.  Authorization to Direct Sublease Payments. Sub-Tenant shall have the right
     to pay all rent and other sums owing by Sub-Tenant to Sub-Landlord
     hereunder for those items which also are owed by Sub-Landlord to Landlord
     under the Lease directly to Landlord if Sub-Tenant reasonably believes that
     Sub-Landlord has failed to make any payment required to be made by Sub-
     Landlord to Landlord under the Lease and Sub-Landlord fails to provide
     adequate proof of payment within two (2) business days after Sub-Tenant's
     written
<PAGE>

     demand requesting such proof. Any sums paid directly by Sub-Tenant to
     Landlord in accordance with this paragraph shall be credited toward the
     amounts payable by Sub-Tenant to Sub-Landlord under the Sublease. In the
     event Sub-Tenant tenders payment directly to Landlord in accordance with
     this paragraph and Landlord refuses to accept such payment, Sub-Tenant
     shall have the right to deposit such funds in an account with a national
     bank for the benefit of Landlord and Sub-Landlord, and the deposit of said
     funds in such account shall discharge Sub-Tenant's obligation under the
     Sublease to make the payment in question.

26.  Assignment of Rights. Sub-Landlord hereby assigns to Sub-Tenant all
     warranties given and indemnities made by Landlord to Sub-Landlord under the
     Lease which would reduce Sub-Tenant's obligations hereunder, and shall
     cooperate with Sub-Tenant to enforce all such warranties and indemnities.

27.  Subordination. Sub-Landlord shall reasonable efforts to obtain from any
     lenders or ground lessors of the Sublease Premises a written agreement in
     form reasonably satisfactory to Sub-Tenant providing for recognition of
     Sub-Tenant's interests under the Sublease in the event of foreclosure of
     the lender's security interest or termination of the ground lease.

28.  Hazardous Materials. To the best knowledge of Sub-Landlord, no Hazardous
     Materials are present in or about the Sublease Premises and no action,
     proceeding, or claim is pending or threatened concerning any Hazardous
     Materials or pursuant to any laws. Sub-Landlord shall indemnify, defend,
     protect and hold Sub-Tenant, its agents, officers, directors and
     shareholders, harmless from and against all claims, losses, costs, damages,
     liabilities, (including, without limitation, sums paid in settlement of
     claims), and expenses (including, without limitation, reasonable attorneys'
     and consultant's fees and litigation expenses), arising out of or based
     upon the presence of any Hazardous Materials on, under, in or about the
     Sublease Premises, except to the extent the same results from Sub-Tenant's,
     or any other person or entity's, release or emission of Hazardous Materials
     in or about the Sublease Premises.
<PAGE>

29.  Approvals. Whenever the Sublease requires an approval, consent,
     designation, determination, selection or judgment by either Sub-Landlord or
     Sub-Tenant, unless another standard is expressly set forth, such approval,
     consent, designation, determination, selection or judgment and any
     conditions imposed thereby shall be reasonable and shall not be
     unreasonably withheld or delayed and, in exercising any right or remedy
     hereunder, each party shall at all times act reasonably and in good faith.

30.  Landlord Consent. The Sublease shall be conditioned upon receipt of consent
     thereto by Landlord in a form reasonably acceptable to Sub-Tenant, which
     consent shall, at Sub-Tenant's election, include the terms set forth in
     Exhibit "C" hereto. Sub-Landlord shall use commercially reasonable efforts
     to obtain such consent. In the event Landlord fails to so consent within
     thirty (30) days for the date Sub-Tenant executes the Sublease, either Sub-
     Landlord or Sub-Tenant shall have the right to terminate the Sublease at
     any time before such consent is received by delivering written notice
     thereof to the other party.

     IN WITNESS WHEREOF, the parties hereto have caused this Sublease to be
executed and sealed by their respective representatives, thereunto duly
authorized, as of the date first above written.

                         Sub-Landlord:

                         Williams Communications Inc.,

                         By:  /s/ James A. Wootten
                              --------------------

                         Printed: James A. Wootten
                                  ----------------

                         Title:  Vice President
                                 -----------------

ATTEST:

-----------------
Secretary [Seal]
<PAGE>

                         Sub-Tenant:

                         Concentric Network Corporation

                         By:  /s/ Henry R. Nothhaft
                              ---------------------------

                         Printed:  Henry R. Nothhaft
                                   ----------------------

                         Title: Chairman, President & CEO
                               --------------------------

ATTEST:

--------------------
Secretary [Seal]
<PAGE>

                                   EXHIBIT B

                         Williams Technology Solutions
                         Anglum Leasehold Improvements
                                1997 Relocation


                                          Net Book Value
     Phase I
          Office Buildout                    $ 76,829.22
          Electrical                         $ 63,941.84
          Kitchen-New Cabinets/Counter       $    630.63
          Net Ops/Computer Room              $ 31,966.17
          Security/Fire Protection           $ 16,713.87
                                             -----------
                    Sub-total                $190,081.73

     Phase II
          Construction                       $ 58,102.50
          Floor Covering                     $ 16,288.64
          Electrical                         $ 50,471.02
          HVAC                               $  4,383.86
          Signage                            $  5,579.46
          Misc.                              $  1,092.78
                                             -----------
                    Sub-total                $135,918.27
                                             -----------

                    Total                    $326,000.00
                                             ===========
<PAGE>

                                   Exhibit B


5 ton Liebert cooling system w/Humidification

30 KVA UPS
<PAGE>

                                     LEASE


THIS LEASE, made and entered into the 26 day of February, 1997, by and between
ARMSTRONG PROPERTIES, LTC, a Missouri Limited Partnership ("Landlord"), and
CRITICAL TECHNOLOGIES, INC., a Missouri corporation ("Tenant"),


                                  WITNESSETH:

1.   PREMISES: Landlord, for and in consideration of the rents, covenants and
     --------
     agreements hereinafter mentioned and hereby agreed to be paid, kept and
     performed by Tenant, does hereby lease with covenant for quiet enjoyment to
     Tenant, and Tenant hereby hires from the Landlord, the following described
     premises (the "Leased Premises") located in the city of Hazelwood, in the
     County of St. Louis, State of Missouri, and more particularly described as
     follows:

          A 23,500 square foot office building and adjoining parking areas known
          and numbered as 944 Anglum Drive, Hazelwood, Missouri 63042.

2.   USE OF PREMISES: The Leased Premises may be used and occupied by Tenant
     ---------------
     during the term hereof, subject to the conditions herein contained and
     subject to applicable zoning regulations, for parking, office and warehouse
     activities. In no event shall the leased Premises be used for any purpose
     contrary to law, zoning regulations, or recorded restrictions, if any.

3.   IMPROVEMENTS TO PROPERTY: Landlord agrees that prior to the commencement of
     ------------------------
     the term of this Lease it will, at its expense, inspect and repair all of
     the mechanical (heating, cooling and ventilating) units, lighting,
     electrical, plumbing, and windows, in order to place same in good working
     order. Landlord shall not be obligated to make any other repairs or
     improvements to accommodate Tenant's use. Tenant shall have the right to
     install in the Leased Premises additional heating ventilating and air
     conditioning equipment, loading facilities, interior furnishes and shall
     have the right to instill a free-standing electrical generator outside of
     the building, provided all of the following conditions have been met: (a)
     plans and specifications for any such improvement shall have been submitted
     to Landlord and Landlord shall have specifically approved same in writing
     (which approval Landlord agrees shall not be unreasonably withheld) and (b)
     all work is done in a good and workmanlike manner in accordance with the
     plans and specifications approved by Landlord, (c) all work is done in
     full compliance with all building codes, City of Hazelwood ordinances and
     other laws applicable thereto, and (d) Tenant shall pay for all cost and
     expense involved in such work, including and professional fees incurred by
     Landlord to review such plans and specifications, and (e) Tenant shall
     obtain Lien Waivers from all mechanics and material suppliers for such
     improvements.

4.   TERM: The term of this Lease shall commence on the 26th day of February,
     ----
     1997, and end on the 31st day of March, 2002, both dates inclusive. If by
     mutual consent of the parties, Tenant shall remain in possession of the
     Leased Premises after the expiration of the term of this Lease, such
     possession shall be as a month-to-month tenant, during which the rent shall
     be payable at the same rate as that in effect during the last month of the
     term, and provisions of this Lease shall be applicable.

5.   RENT: Tenant shall, without deduction, abatement or set-off of any nature
     ----
     whatsoever, pay to Landlord as fixed rent for the Leased Premises, as
     follows. There shall be no rent paid for the period of February 26, 1997
     to March 31, 1997.

          Commencing April 1, 1997 to March 31, 1998 = $11,750.00 per month
          Commencing April 1, 1998 to March 31, 1999 = $12,729.00 per month
          Commencing April 1, 1999 to March 31, 2000 = $14,687.00 per month
          Commencing April 1, 2000 to March 31, 2002 = $16,645.00 per month


                                  Page 1 of 8
<PAGE>

     payable in advance without demand on the first day of each and every month
     during the term of this Lease, commencing April 1, 1997. Tenant shall pay
     the fixed rent for April, 1997 upon the execution hereof.

     A late charge of five percent (5%) of any monthly rental payment will be
     added after fifteen (15) days from the due date. Failure to pay any monthly
     rental within ten (10) days after the due date shall be deemed to be an
     event of default by Tenant under this Lease.

6.   SECURITY DEPOSIT: Upon the execution of this Lease, Tenant shall deposit
     ----------------
     with Landlord the sum equal to $28,395.00 of which $11,750.00 shall be
     credited against the first month's rent payable hereunder and the balance
     of $16,645.00 shall be held by Landlord as security for the faithful
     performance and observance by Tenant of all the terms, covenants and
     conditions of this Lease. Landlord shall retain said funds, as its own,
     (without being liable for interest thereon) and may use, apply or retain
     the whole or any part of the funds so deposited to the extent required for
     the payment of any rent, additional rent or other sums as to which Tenant
     is in default, or for the payment of any amount which Lessor may be
     required to expend by reason of Tenant's default in respect of any of the
     terms of this Lease. Landlord shall give Tenant five (5) days' written
     notice before applying the deposit to any default. Should Tenant comply
     with all of the terms of this Lease, so much of said security deposit not
     spent or applied pursuant to the provisions of this paragraph shall be
     returned to Tenant within thirty (30) days after the termination of this
     Lease. If any portion of said deposit is so used or applied, Tenant shall,
     within ten (10) days after the demand therefor, deposit cash with Landlord
     in an amount sufficient to restore the security deposit to its original
     amount and Tenant's failure to do so shall be a material breach of this
     Lease. Should Landlord sell its interest in the Premises during the term
     hereof and if Landlord delivers to the purchaser thereof the then
     unappropriated funds deposited by Tenant as aforesaid, thereupon Landlord
     shall be discharged from any and all liability, with respect to said
     security deposit. The security deposit may not be used to pay the last
     month's rent.

7.   TAXES: Tenant shall pay all real estate and occupancy taxes, assessments
     -----
     and/or installments thereof on or before the date the same become due,
     whether general or special, foreseen and unforseen, and shall furnish
     Landlord a copy of the paid receipts therefor. Taxes shall be prorated for
     1997 and 2002 for the period of the Lease.

     Tenant reserves the right and privilege to contest the validity and amount
     of any tax or assessment payable by it to any governmental body or agency,
     whether assessed in its name or in the name of the Landlord. Landlord
     grants Tenant the right to contest the validity and amount of any such tax
     or assessment provided Tenant pays all costs and fees incurred in
     proceedings before any agency or court; and, provided further, that Tenant
     shall make proper provision to prevent any such tax or assessment from
     becoming delinquent by reason of any contest thereof.

8.   ASSIGNMENT AND SUBLETTING: Tenant shall not assign this Lease nor sublet
     -------------------------
     all or any part of the Leased Premises without the prior written consent of
     Landlord, which consent shall not be unreasonably withheld. Landlord's
     consent to one assignment or subletting shall not be deemed a consent to
     any other or further assignment or subletting. No assignment of this Lease
     or subletting thereunder and no acceptance by Landlord of any rent or any
     other sum of money from any assignee or sublessees shall release Tenant
     from any of its obligations under this Lease; and in any event Tenant shall
     remain primarily liable on this Lease for the entire term hereof and shall
     in no way be released from the full and complete performance of all the
     terms, conditions, covenants and agreements herein contained.

9.   PARKING: Tenant shall during the Lease term have exclusive right to use all
     -------
     of the parking spaces.

10.  REPAIRS AND MAINTENANCE: Landlord shall, at its cost, during the term of
     -----------------------
     this Lease keep in good repair the foundations, exterior walls, roofs,
     gutters, and down spouts forming a part of the Leased Premises.

     Landlord will be responsible for making major repairs or replacement of the
     HVAC system until March 31, 1999, at which time Tenant will be responsible
     for HVAC repairs or


                                  Page 2 of 8
<PAGE>

     replacement throughout the remainder of the Lease, as required. Tenant
     shall, at its cost, keep in good repair the parking lot drives, sidewalks,
     and common areas forming a part of the Leased Premises and shall maintain
     in good and first-class condition the lawn, sidewalks, drives, common
     areas, and shrubbery, including watering same, cutting the grass, and the
     replacing of any dead trees, bushes or other ornamental plants.

     Tenant also, at its own cost and expense, keep all other parts of the
     Leased Premises in good repair (including, but not limited to, repair and
     replacement of the mechanical equipment, plumbing system, electrical
     system, sprinkler system, exterior doors and interior doors and partitions)
     and shall keep the Leased Premises in good order to the standards of a
     first-class office building, including, but in no way limited to, keeping
     the Leased Premises free of trash; and maintaining, and replacing all
     broken glass, plate glass and skylights, in the Leased Premises.

     In the event that Tenant shall be in default under this Paragraph 10, then
     Landlord may cure such default on behalf of Tenant after providing 10 days
     prior written notice, in which event Tenant on demand shall reimburse
     Landlord for all sums paid to effect such cure, plus twelve percent (12%)
     thereof to cover Landlord's overhead expenses and plus reasonable
     attorneys' fees. In order to collect such reimbursement, Landlord shall
     have all the remedies available under this Lease for a default in the
     payment of rent.

11.  ALTERATIONS: No substantial alteration, addition or improvement to the
     -----------
     Leased Premises shall be made by Tenant without the written consent of
     Landlord, such consent not to be unreasonably withheld. Any alteration,
     addition, or improvement made by Tenant after such consent shall have been
     given, and any non-movable fixtures installed as a part thereof, shall at
     Landlord's option become the property of Landlord upon the expiration or
     sooner termination of this Lease; provided, however, that Landlord shall
     have the right to require Tenant to remove such fixtures including all
     phone, computer and telecommunications cabling, at Tenant's cost upon such
     termination of this Lease. It is expressly understood and agreed, however,
     that Tenant shall retain ownership of, and shall upon termination of this
     Lease be permitted to remove from the Leased Premises, those items of
     equipment and personal property described on Exhibit A attached hereto,
                                                  ---------
     provided that such removal does not adversely affect or impair the
     structure of the Leased Premises or mechanical or working systems serving
     the Leased Premises, and further provided that Tenant shall be responsible
     at its sole cost for repairing all damage to the Leased Premises caused by
     such removal.

12.  WASTE: Tenant covenants not to do or suffer any waste to the Leased
     -----
     Premises.

13.  MECHANICS' LIENS: Tenant shall not permit mechanics' liens to be filed
     ----------------
     against the fee of the Leased Premises or against Tenant's leasehold
     interest in the Premises by reason of work, labor, services or materials
     supplied or claimed to have been supplied to Tenant or anyone holding the
     Leased Premises through or under Tenant, whether prior or subsequent to the
     commencement of the term hereof. If any such mechanics' lien shall at any
     time be filed, against the Leased Premises and Tenant shall fail to remove
     same within thirty (30) days thereafter, it shall constitute a default
     under the provisions of this Lease.

14.  RESTRICTIONS OF USE: Tenant shall not allow, permit or suffer any noise,
     -------------------
     smoke or odor to escape from the Leased Premises, or occupy the Leased
     Premises in such manner as to constitute a public nuisance or environmental
     hazard. No sign, fixture, advertisement or notice shall be displayed,
     inscribed, painted, or affixed by Tenant on any part of the outside of the
     Leased Premises or on the parking lot or on any part of the Leased
     Premises' without the prior written consent of Landlord. At the expiration
     of the Lease term, Tenant shall remove all such signs or advertisement
     matter at its cost and shall repair any damage resulting from such removal.
     Nor shall Tenant allow or permit any goods, materials or equipment to be
     stored outside of the buildings without the prior written consent of
     Landlord. Such consent may not be unreasonably withheld.

15.  UTILITIES: Tenant shall pay for all gas, electricity, water, air
     ---------
     conditioning, sewer and telephone service and all other utilities used in
     and upon the Leased Premises. Tenant shall be responsible for its own trash
     removal.


                                  Page 3 of 8
<PAGE>

16.  ACCESS: Landlord, and its duly authorized agents, employees and
     ------
     contractors, shall have access to the Leased Premises at all reasonable
     times for the purpose of inspecting the same and making necessary repairs
     or replacements as described under Paragraph 10.

17.  INSURANCE: Prior to commencement of occupancy by Tenant, Tenant at its
     ---------
     expense shall obtain a policy of insurance insuring the Leased Premises
     against losses for fire and extended coverage for the full replacement
     value of the building on the Leased Premises including earthquake, coverage
     and shall also obtain a policy of public liability insurance in at least
     the amount of $1,000,000.00. Landlord shall be named as an insured under
     such policies. In the event the building and improvements on the Leased
     Premises are damaged or destroyed by fire or other casualty, rent shall not
     abate and Landlord shall restore the said premises to substantially the
     same condition in which they existed prior to such damage, and with all
     reasonable speed and promptness, not to exceed one hundred eighty (180)
     days. Landlord shall use the proceeds of such insurance and repairs in
     rebuilding the Leased Premises. In determining what constitutes reasonable
     speed and promptness, considerations shall be given to delays caused, by
     strikes, adjustment of insurance, and other causes beyond Landlord's
     control. In no event shall Landlord be required to restore any alteration,
     additions, or improvement made by or for Tenant, nor any trade fixtures,
     equipment or other property belonging to Tenant. In the event that the
     Leased Premises have not been restored within one hundred eighty (180) days
     of the casualty, either Tenant or Landlord may thereafter elect to
     terminate this Lease by serving written notice of termination on the other
     party, provided that the Leased Premises have not been restored prior to
     the date on which the notice of termination has been given hereunder.
     Tenant shall have the right to provide the insurance policies required
     above pursuant to blanket policies obtained by Tenant, provided such
     blanket policies expressly afford coverage to the Premises and Landlord
     required by this Lease. Landlord and Tenant hereby waive the right each
     may have against the other on account of any loss or damage occasioned to
     Landlord or Tenant, as the case may be, their respective property, the
     Leased Premises or its contents arising from any risk insured against by
     Landlord or Tenant; and the parties each, on behalf of their respective
     insurance companies insuring the property of either Landlord or Tenant
     against any such loss, waive any right of subrogation that it may have
     against Landlord or Tenant, as the case may be. This release shall apply
     only to the extent that such loss or damage is covered by insurance and
     only so long as the applicable insurance policies contain a clause or
     otherwise provide that this release shall not affect the right of the
     injured to recover under such policies.

18.  LIABILITY: Landlord shall not be liable for any failure of water supply,
     ---------
     gas, or electric current; nor for any injury or damage to person or
     property caused by gasoline, oil, steam, gas electricity, ice/snow,
     tornado, flood, wind, or similar storms and disturbances; nor water or rain
     which may leak or flow from the street, sewer, gas mains or any subsurface
     area from any part of the buildings or improvements on the Leased Premises
     occurring from such causes or at no fault of Landlord; nor for any
     interference with light or air. Landlord shall not be liable for any
     personal injury to Tenant, its officers, agents, employees and invitees,
     nor for any damages to any property of Tenant, irrespective of how much
     such injury or damage may be caused.

     Tenant shall indemnify and hold Landlord harmless from any loss, damages,
     and expenses incident thereto, including attorneys' fees, arising out of
     the liability to any person on account of loss of or damage to property or
     injury persona resulting item the use and occupancy of the Leased Premises
     or the parking lot, sidewalks, XXX, or common areas by Tenant; except,
     however, Tenant shall not indemnify Landlord for its own acts of
     negligence.

19.  CONDEMNATION
     ------------

     (a)  If the whole of the Leased Premises shall be taken for any public or
          any quasi-public use under any statute or by right of eminent domain,
          or by purchase under threat of condemnation, then this Lease shall
          automatically terminate as of the date that title shall be taken. If
          any part of the Leased Premises shall be so taken as to render the
          remainder thereof unusable for the purposes for which the Leased
          Premises were leased in either parties' discretion, then Landlord and
          Tenant shall each have the right to terminate this Lease on thirty
          (30) days' notice to the other given within ninety (90) days after the
          date of such taking. In the event that this Lease shall terminate or
          be


                                  Page 4 of 8
<PAGE>

          terminated, the rental shall, if and as necessary, be prorated between
          Landlord and Tenant as of the date of such termination;

     (b)  If any part of the Leased Premises shall be so taken and this Lease
          shall not terminate or be terminated under the provisions of
          Subparagraph (a) above, then the rental shall be equitably apportioned
          according to the area so taken, and Landlord shall, at its own cost
          and expense, restore the remaining portion of the Leased Premises to
          the extent necessary to render them reasonably suitable for the
          purposes for which they were leased, and shall make all repairs to the
          building in which the Leased Premises are located to the extent
          necessary to constitute the building a complete architectural unit;
          and

     (c)  All compensation awarded or paid upon such a total or partial taking
          of the Leased Premises shall belong to and be the property of Landlord
          without any participation by Tenant; provided, however, that nothing
          contained herein shall be construed to preclude Tenant from
          prosecuting any claim directly against the condemning authority in
          such condemnation proceeding for loss of business, depreciation to,
          damage to, or cost of removal of, or the value of stock, trade
          fixtures, furniture, and other personal property belonging to Tenant;
          provided, however, that no such claim shall diminish or otherwise
          adversely affect Landlord's award.

20.  DEFAULT: The following events shall be deemed to be events of default by
     -------
     Tenant under this Lease: (i) if Tenant shall fail to pay any fixed or
     additional rent hereby reserved within ten (10) days after due date; (ii)
     if Tenant shall fail to comply with any term, or provision, or covenant of
     this Lease, other than the payment of rent, and shall not cure such failure
     within thirty (30) days after written notice thereof to Tenant; (iii) if
     Tenant shall become insolvent, or shall make a transfer with intent to
     defraud its creditors, or shall make an assignment for the benefit of its
     creditors; (iv) if Tenant shall file a petition under any section or
     chapter of the National Bankruptcy Act; as amended, or under any similar
     law or statute of the United States or any state thereof; or Tenant shall
     be adjudicated bankrupt or insolvent in proceedings filed thereunder; (v)
     if a receiver or trustee shall be appointed for all or substantially all of
     the assets of Tenant; or (vi) if Tenant shall desert or vacate any
     substantial portion of the Leased Premises.

     Upon the occurrence of any such event of default, Landlord shall have the
     option to pursue any one or more of the following remedies (as well as any
     other remedies provided by law) without any further notice or demand
     whatsoever:

     (a)  Declare immediately due and payable the entire amount of the rent then
          remaining to be paid under this Lease for the balance of the Lease
          term;

     (b)  Enter upon and take possession of the Leased Premises by any lawful
          means, and dispossess, expel, and remove Tenant and any other persons
          who may be occupying the Leased Premises or any part thereof
          (including changing or altering the locks and other security devices)
          and remove and expel any personal property or trade fixtures located
          therein, all without being liable to any prosecution thereof or for
          any damages resulting therefrom. Such re-entry and/or repossession by
          Landlord shall not terminate this Lease nor relieve Tenant of its
          obligations under this Lease, including its obligation to pay rent
          (whether or not the time for payment of rent has been accelerated). In
          the event of such re-entry or repossession by Landlord, Landlord shall
          also have the option to re-let the Leased Premises as agent for Tenant
          (in the name of Landlord or in the name of Tenant), at any rent and
          for any term readily obtainable and receive the rent therefor, in
          which event Tenant shall be given credit for any rents that may arise
          by reason, of such re-letting (after first deducting all repossession
          costs, brokerage commissions, legal expenses, attorneys' fees, and all
          other expenses in cleaning, repairing and altering the premises for
          re-letting); and

     (c)  Forfeit and terminate this Lease forthwith. In the event of such
          termination, Tenant shall immediately surrender the Leased Premises to
          Landlord and if Tenant fails to do so, Landlord may enter upon and
          take possession of the Leased Premises by any lawful means and
          expel or remove Tenant and any other person who may be


                                  Page 5 of 8
<PAGE>

          occupying said premises or any part thereof, and any personal property
          or trade fixtures located therein. In the event of the forfeiture of
          this Lease as herein provided, Tenant agrees that any security deposit
          being held by Landlord hereunder shall be retained by Landlord and
          applied against all damages incurred with respect to Tenant's default,
          which damages shall include all unpaid rent and any other damages
          accruing to Landlord by reason of the violation by Tenant of any of
          the terms, provisions and covenants of this Lease.

     Tenant hereby waives demand for rent, demand for possession, notice for
     forfeiture, notice of termination and any and all other demands or notices
     required by law.

     Pursuit by Landlord of any of the foregoing remedies or any other remedy
     provided by law shall not constitute a forfeiture or waiver of any rent due
     to Landlord hereunder or of any damages accruing to Landlord by reason of
     the violation by Tenant of any of the terms, provisions and covenants of
     this Lease. In no event shall Tenant be relieved from its obligation to pay
     the rentals specified in this Lease by reason of a surrender of possession,
     termination of this Lease or in any other manner whatsoever, unless
     specifically agreed to in writing by Landlord.

     No waiver by Landlord of any violation or breach of any of the terms,
     provisions and covenants of this Lease shall be deemed or construed to
     constitute a waiver of any other violation or breach of any of the terms,
     provisions and covenants herein contained. Forbearance by Landlord to
     enforce one or more of the remedies herein provided upon an event of
     default shall not be deemed or construed to constitute a waiver of such
     default.

     If Landlord incurs any expenses, including court costs and attorneys' fees,
     as a result of a default by Tenant under this lease, then such expenses
     shall be reimbursed by Tenant as additional rent, whether or not such
     default is subsequently cured.

     Tenant's delinquent payments shall bear interest at the rate of twelve
     percent (12%) per annum from the date of delinquency until paid.

21.  SURRENDER AND TERMINATION: At the expiration of the Lease term, Tenant
     -------------------------
     shall surrender the Leased Premises in as good condition as they were in at
     the beginning of the term, reasonable use and wear and damage by the
     elements excepted.

     Notwithstanding and provisions of law or any judicial decision to the
     contrary, no notice shall be required to terminate the term of this Lease
     as herein provided, and the term of this Lease shall expire on this
     termination date herein mentioned without notice being required from either
     party. In the event that Tenant or any party holding under Tenant shall
     remain in possession of the Leased Premises beyond the expiration of the
     term of this Lease, whether by limitation or forfeiture, such party shall
     pay double rent hereunder during such hold-over period, except if such
     hold-over is with Landlord's consent as provided in Paragraph 4.

22.  NOTICES: Any notice required to be given by either party to the other party
     -------
     under the terms of this Lease shall be personally served upon it or mailed
     by United Stated certified mail to said party at its last known address.
     The current addresses of the parties are as follows:

          LANDLORD                                   TENANT
          --------                                   ------
          Mr. William H. Armstrong, Jr.              Mr. Mike Fallon, Treasurer
          Armstrong Properties, LTC                  Critical Technologies, Inc.
          31 Fordyce                                 3324 Hollenberg Drive
          St. Louis, Missouri 63124                  Bridgeton, Missouri 63044

23.  HEADINGS AND DEFINITIONS:
     ------------------------

     (a)  It is agreed that the headings and phrases as to the contents of
          particular paragraphs of this Lease are inserted a matter of
          convenience and for reference, and in no way are or are intended to be
          a part of this Lease or in any way to define, limit or describe the
          scope or intent of the paragraph to which they refer; and


                                  Page 6 of 8
<PAGE>

     (b)  Where in this instrument pronouns appear, or words indicating the
          singular number, such words shall be considered as masculine,
          feminine, or neuter pronouns or words indicating the plural number,
          and vice versa, where the context indicates the propriety of such use.

24.  MODIFICATIONS: Landlord and Tenant agree that this Lease contains the
     -------------
     entire agreement between them and shall not be modified in any manner
     except by an instrument in writing signed by each of them.

25.  BENEFIT: This Lease shall inure to the benefit of and be binding upon
     -------
     Landlord and Tenant and their respective heirs, executors, personal
     representatives, administrators, successors and assigns, as the case may
     be.

26.  SUBORDINATION: Tenant agrees that upon delivery to it by any mortgagee of
     -------------
     the Leased Premises of a "non-disturbance letter," as same is defined
     below, that this Lease and Tenant's interest in this Lease shall be
     subordinated to any mortgage, deed of trust or other method of financing or
     refinancing now or hereafter encumbering the Leased Premises, the land
     underlying the Leased Premises, and/or the building of which the Leased
     Premises comprise a part; and to all renewals, modifications, replacements,
     consolidations and extensions thereof. Tenant further agrees that in such
     event it will execute and deliver any and all documents necessary to
     evidence the subordination of its rights under this Lease as aforesaid. The
     "non- disturbance letter" referred to above shall be any letter from the
     holder of such mortgage, deed of trust or other security instrument to the
     effect that in the event of a foreclosure or other action taken under any
     such security instrument that this Lease and the rights of Tenant hereunder
     shall not be disturbed, diminished or interfered with, but shall continue
     in full force and effect so long as Tenant shall not be in default
     hereunder.

     In any event, if any such mortgage, deed of trust or other security
     instrument encumbering the Leased Premises is foreclosed for any reason,
     and the holder of such mortgage, deed of trust or other security instrument
     succeeds to the interest of Landlord under this Lease, Tenant shall be
     bound to such mortgage, deed of trust or security holders under all of the
     terms of this Lease for the balance of the term thereof remaining, with the
     same force and effect as if said mortgagee were the Landlord under this
     Lease; and Tenant hereby attorns to the mortgagee as its Landlord, such
     attornment to be effective and self-operative, without the execution of any
     further instrument on the part of either of the parties hereto, immediately
     upon the mortgage succeeding to the interest of Landlord under this Lease.

27.  ESTOPPEL CERTIFICATE: Tenant agrees, at any time, and from time to time,
     --------------------
     upon not less than ten (10) days' prior notice by Landlord, to execute,
     acknowledge and deliver to Landlord, a statement in writing addressed to
     Landlord certifying that this Lease is unmodified and in full force and
     effect (or, if there have been modifications, that the same is in full
     force and effect as modified and stating the modifications), stating the
     dates to which the fixed minimum rent, additional rental and other charges
     have been paid, and stating whether or not to the best knowledge of the
     signer of such certificate, agreement, term, provision or condition
     contained in this Lease, and, if so, specifying each such default of which
     the signer may have knowledge, it being intended that any such statement
     delivered pursuant hereto may be relied upon by Landlord and by any
     mortgagee or prospective mortgagee of any mortgage affecting the building
     or the building and the land, and by prospective purchaser of the Property.

28.  SEVERABILITY: This Lease and its provisions are to be construed as a whole,
     ------------
     but should any provision be held or be void or illegal, then such clause or
     provision shall be deemed severable from the Lease and shall be considered
     stricken herefrom, but the Lease shall not be deemed void or otherwise
     modified or affected.

29.  QUIET ENJOYMENT: Tenant shall at all times during the term hereof and all
     ---------------
     extensions or renewals, subject only to its payment of the rental and
     performance of the agreements on its part to be performed, peacefully and
     quietly have, hold and enjoy the premises without any manner of suit,
     trouble, hindrance or from Landlord, its successors or assigns, or any
     other person.


                                  Page 7 of 8
<PAGE>

30.  ENVIRONMENTAL: Tenant shall not use, store, manufacture, dispose of or
     -------------
     discharge any pollutants, contaminants, or harmful or hazardous substances
     from or on the Leased Premises or otherwise occupy or permit the Leased
     Premises to be occupied or used in a manner which (i) violates any law,
     regulation, rules or other governmental requirement, (ii) impairs the
     health, safety or condition of any person or property or (iii) adversely
     affects the use, enjoyment or value of the Leased Premises or the
     surrounding property. Tenant shall promptly notify Landlord of the breach,
     or the potential or threatened breach, of any of the provisions of this
     paragraph. Tenant shall indemnify and hold Landlord and its officers,
     shareholders, partners, employees, and agents, harmless from any loss,
     claim, liability or expense (including, without limitation, attorneys'
     fees, court costs, consultant fees, expert fees, penalties, fines, removal,
     clean-up, transportation, disposal and restoration expenses) arising in
     connection with Tenant's failure to comply with the provisions of this
     paragraph. A breach of the provisions of this paragraph shall be a material
     default enabling Landlord to exercise any of the remedies set forth in this
     Lease. Tenant's obligation hereunder shall survive the termination of this
     Lease.

31.  RENEWAL OPTION: Tenant shall have the right to extend the term of the Lease
     --------------
     for an additional period of three (3) years, commencing on the expiration
     of the original term of the Lease. Such renewal option shall be deemed
     effectively exercised only if Tenant has given Landlord written notice
     thereof at least one hundred eighty (180) days prior to the expiration of
     the original term and only if Tenant is not in default under this Lease
     both at the time of such exercise and at the time of the commencement of
     the renewal term. All terms and provisions of the Lease shall be applicable
     during such renewal term, except the fixed rent payable pursuant to
     paragraph 5 shall equal $223,250.00 annually, with equal monthly payments
     of $18,604.17. Such rent shall be payable without deductions, abatements or
     set-offs of any nature whatsoever. It is expressly understood that the
     renewal option granted in this paragraph is personal to the entity
     expressly named as Tenant in this Lease and to any assignee and subtenant
     which has been approved by Landlord, and that said option shall terminate
     upon an assignment or subletting of Tenant's interest hereunder and shall
     not inure to the benefit of any assignee or subtenant of Tenant which has
     not been approved by Landlord.

32.  CANCELLATION OPTION: Upon six months prior written notification, Leasee
     -------------------
     will have the right to terminate this Lease at the end of the 36th month.
     Anytime after 36 months Leasee can terminate this Lease with three months
     prior written notice. As consideration, Leasee will pay Lessor, an amount
     equal to 50% of the remaining fixed rent obligation under the Lease as of
     the effective date of the Lease termination, which amount will accompany
     and be a requirement of the notice to terminate.

This Lease consists of thirty-two (32) paragraphs numbered consecutively.

IN WITNESS WHEREOF, the parties hereto have hereunto set their hands the day and
year first above mentioned.

TENANT:                             LANDLORD:

CRITICAL TECHNOLOGIES, INC.         ARMSTRONG PROPERTIES, LTC


By: /s/ [ILLEGIBLE]^^               By: /s/ William H Armstrong, Jr.
    --------------------                ----------------------------------------
                                        Wm. H. Armstrong, Jr., General Partner

Date:   2/27/97                     Date:  2/27/97
      ------------------                   -------------------------------------

Time:   12:00 pm                    Time:  1:30 pm
      ------------------                   -------------------------------------


                                  Page 8 of 8