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                                                                  EXHIBIT 10.156

               AMENDMENT NO. 3 TO CREDIT AND SECURITY AGREEMENT
               ------------------------------------------------

     THIS AMENDMENT NO. 3 TO CREDIT AND SECURITY AGREEMENT (this "Agreement")
made as of the 17th day of October, 2000, by and among APPLIED BIOSCIENCE
INTERNATIONAL INC., a Delaware corporation, its successors and assigns (the
"Lender"), ENVIRON HOLDINGS, INC., a Delaware corporation ("EHI"), ENVIRON
INTERNATIONAL CORPORATION (formerly APBI Environmental Sciences Group, Inc.), a
Virginia corporation ("EIC" together with EHI the "Original Borrowers"), and
ENVIRON FACILITY SERVICES CORPORATION, a Virginia corporation (the "New
Borrower"), jointly and severally (the Original Borrowers and the New Borrower,
each a "Borrower", and collectively, the "Borrowers").

                                   RECITALS
                                   --------

     A.  The Original Borrowers are parties to a certain Credit and Security
Agreement, along with the Lender dated February 2, 1999 (as thereafter amended,
modified, restated, substituted, extended and renewed from time to time, the
"Credit Agreement"), pursuant to which the Lender agreed to make available
certain credit facilities consisting of (i) a revolving credit facility (the
"Revolving Credit Facility") to provide working capital to the Original
Borrowers, (ii) a term loan (the "Term Loan") in the amount of Seven Million
Dollars ($7,000,000) to be used to pay a portion of the Purchase Price (as
defined in the Credit Agreement), (iii) letters of credit ("Letters of Credit")
to be used for general corporate purposes by the Original Borrowers, and (iv) an
acquisition loan in the amount of Eighteen Million Dollars ($18,000,000), also
to pay a portion of the Purchase Price.  As set forth in that certain Amendment
No. 2 and Restatement of Credit and Security Agreement dated November 24, 1999
by and among Lender and the
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Original Borrowers, the Term Loan has been satisfied and the Lender has no
obligation to make any loans under the Revolving Credit Facility or to issue any
Letters of Credit to or for the benefit of the Original Borrowers under the
Credit Agreement.

     B.  Pursuant to a plan of corporate restructuring approved by EIC's Board
of Directors, EIC has created a separate legal entity for its Facilities Group
in the form of the New Borrower and has transferred all of its assets related to
the Facilities Group to the New Borrower pursuant to that certain Asset Purchase
Agreement dated January 1, 2000 by and between EIC and the New Borrower (the
"Facilities Group Spin Off") and the Borrowers have requested that the Lender
consent to the Facilities Group Spin Off and the Lender has consented on the
condition, among others, that the parties hereto execute this Agreement.

     C.  The parties hereto desire to add the New Borrower as a party to the
Credit Agreement and to make certain other amendments to the Credit Agreement,
all as more fully set forth in this Agreement.

     NOW, THEREFORE, in consideration of the foregoing, and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Borrowers and the Lender do hereby agree as follows:

     1.  Recitals. The parties hereto acknowledge and agree that the above
         --------
Recitals are true and correct in all material respects and that the same are
incorporated herein and made a part hereof by reference.

     2.  Defined Terms. Capitalized terms used herein and not otherwise defined
         -------------
shall have the meanings ascribed to them in the Credit Agreement.

     3.  Grant of Security Interest. The New Borrower hereby assigns, pledges
         --------------------------
and grants to the Lender, and agrees that the Lender shall have a perfected and
continuing security interest

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in, and lien on, all of the New Borrower's Collateral. The New Borrower
individually represents and warrants to the Lender that its principal place of
business and the addresses where the Collateral is kept is as set forth on
Schedule 3.23 attached hereto.
-------------

     4.  Assumption of Obligations. The New Borrower promises and agrees to
         -------------------------
perform each and all of the covenants, agreements and obligations in the Credit
Documents to be performed by the Original Borrowers, at the times, in the manner
and in all respects as provided therein, and to be bound by each and all of the
terms and provisions of the Credit Agreement as though the Credit Agreement had
originally been jointly and severally made by the Original Borrowers and the New
Borrower. All of the Borrowers shall remain liable for the performance of each
and all of the covenants, agreements and obligations in the Credit Documents to
be performed by the Borrowers. All references in the Credit Agreement and in any
of the Credit Documents to the "Borrower", the "Borrowers" or the "Obligors"
shall hereafter be deemed to include the New Borrower.

     5.  Consent to Facilities Group Spin Off. The Lender hereby waives any
         ------------------------------------
default or Event of Default occurring under Sections 5.07, 5.10 or 5.12 of the
Credit Agreement occurring solely as the result of the Facilities Group Spin
Off.  The parties acknowledge and agree that the Collateral sold to the New
Borrower pursuant to the Facilities Group Spin Off is and remains subject to the
security interests in the Collateral previously granted to the Lender under the
Credit Agreement.

     6.  Representations and Warranties. The New Borrower hereby issues, makes,
         ------------------------------
ratifies and confirms the representations, warranties and covenants contained in
the Credit Documents as of the date hereof, and further represents, warrants and
covenants to the Lender as follows:

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          (a)  Good Standing. The New Borrower (a) is a corporation duly
               -------------
organized, existing and in good standing under the laws of the jurisdiction of
its creation, (b) has the power to own its property and to carry on its business
as now being conducted, and (c) is duly qualified to do business and is in good
standing in each jurisdiction in which the character of the properties owned by
it therein or in which the transaction of its business makes such qualification
necessary.

          (b)  Power and Authority. The New Borrower has full power and
               -------------------
authority to execute and deliver this Agreement and each of the other Credit
Documents executed and delivered by it, to make the borrowing hereunder, and to
incur the Obligations, all of which have been duly authorized by all proper and
necessary corporate or company action. No consent or approval of stockholders or
of any public authority is required as a condition to the validity or
enforceability of this Agreement or any of the other Credit Documents executed
and delivered by the New Borrower.

          (c)  Binding Agreements. This Agreement and each of the other Credit
               ------------------
Documents executed and delivered by the New Borrower have been properly executed
by the New Borrower, constitute valid and legally binding obligations of the New
Borrower, and are fully enforceable against the New Borrower in accordance with
their respective terms.

          (d)  Litigation. There are no proceedings pending or, so far as the
               ----------
New Borrower knows, threatened before any court or administrative agency which
will materially adversely affect the financial condition or operations of the
New Borrower, or the authority of any Borrower to enter into this Agreement or
any of the other Credit Documents executed and delivered by the New Borrower.

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          (e)  No Conflicting Agreements. There is (a) no charter, by-law, or
               -------------------------
preference stock provision of the New Borrower and no provision of any existing
mortgage, indenture, contract or agreement binding on the New Borrower or
affecting its property, and (b) to the knowledge of the New Borrower, no
provision of law or order of court binding upon the New Borrower, which would
conflict with or in any way prevent the execution, delivery, or performance of
the terms of this Agreement or of any of the other Credit Documents executed and
delivered by the New Borrower or which would be violated as a result of such
execution, delivery or performance.

          (f)  Wholly Owned Subsidiary.  New Borrower is a wholly owned
               -----------------------
subsidiary of EHI.

     7.   Solvency. The Borrowers represent that the fair saleable value of the
          --------
Borrowers' assets taken as a whole (including goodwill minus disposition costs)
exceeds the fair value of their liabilities; that no Borrowers are left with
unreasonably small capital after the transactions contemplated by this
Agreement; and the Borrowers are able to pay their debts (including trade debts)
as they mature.

     8.   Revised Schedules. From and after the effective date hereof, Schedules
          -----------------
3.05, 3.09, 3.10, 3.11, 3.12, 3.13, 3.14, 3.16, 3.17, 3.18, 3.19, 3.20, 3.21,
3.22, 3.23, 3.24, 3.25, 3.25A, 3.26, 3.35, 3.39 and 3.43 of the Credit Agreement
are being replaced in their entirety with the Schedules of corresponding number
attached hereto.

     9.   Conditions Precedent. This Agreement shall become effective on the
          --------------------
date the Lender receives the following documents, each of which shall be
satisfactory in form and substance to the Lender:

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          (a)  The Amended and Restated Promissory Note (the "Restated Seller
Note") issued and delivered by the Borrowers in the form of Exhibit A attached
                                                            ---------
hereto and incorporated herein by reference, payable to the order of the Lender
in the original principal amount of $18,000,000.

          (b)  All documents and instruments (including, without limitation,
UCC-1 and UCC-3 Statements) required to be filed, registered or recorded in
order to create in favor of the Lender a perfected first lien in the New
Borrower's Collateral (subject only to Permitted Liens) in form and in
sufficient number for filing, registration, and recording in each office in each
jurisdiction in which such filings, registrations and recordations are required,
together with such evidence as the Lender may deem satisfactory that all
necessary filing fees and all recording and other similar fees and all taxes and
other expenses related to such filings, registrations and recordings will be or
have been paid in full.

          (c)  The Lender shall have received a Certificate dated as of the date
hereof by the Secretary or Assistant Secretary of the New Borrower covering:

               (i)   true and complete copies of the New Borrower's corporate
charter and by-laws and all amendments thereto;

               (ii)  true and complete copies of the resolutions of the New
Borrower's Board of Directors authorizing (i) the execution, delivery and
performance of the Credit Documents, (ii) the borrowing by the New Borrower
under the Credit Agreement, and (iii) the granting of the Liens contemplated by
this Agreement and any of the Credit Documents to which the New Borrower is a
party; and

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               (iii)  the incumbency, authority and signatures of the officers
of the New Borrower authorized to sign this Agreement and the other Credit
Documents to which the New Borrower is a party.

          (d)  Such other information, instruments, opinions, documents,
certificates and reports as the Lender may deem necessary.

          (e)  Pursuant to Section 4.12 of the Credit Agreement, Lender shall
have received payment of its attorneys' fees incurred in connection with the
preparation, review, negotiation and execution of this Agreement and of all
other instruments, certificates and documents related hereto or executed in
connection herewith.

     10.  Replacement Seller Note. The Borrowers shall execute and deliver to
          -----------------------
the Lender on the date hereof the Restated Seller Note in substitution for, and
not satisfaction of, the issued and outstanding Seller Note, and the Restated
Seller Note shall be the "Seller Note" for all purposes of the Credit Documents.
The Seller Note being substituted pursuant to this Agreement shall be marked
"Replaced" and returned to the Borrowers after the execution and delivery of the
Restated Seller Note to the Lender.

     11.  Counterparts. This Agreement may be executed in any number of
          ------------
duplicate originals or counterparts, each of which duplicate original or
counterpart shall be deemed to be an original and all taken together shall
constitute one and the same instrument.

     12.  Credit Documents; Governing Law; Etc. This Agreement is one of the
          ------------------------------------
Credit Documents defined in the Credit Agreement and shall be governed and
construed in accordance with the laws of the Commonwealth of Virginia. The
headings and captions in this Agreement are for the convenience of the parties
only and are not a part of this Agreement.

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     13.  Acknowledgments. The Borrowers hereby confirm to the Lender the
          ---------------
enforceability and validity of each of the Credit Documents. In addition, the
Borrowers hereby agree to the execution and delivery of this Agreement and the
terms and provisions, covenants or agreements contained in this Agreement shall
not in any manner release, impair, lessen, modify, waive or otherwise limit the
liability and obligations of the Borrowers under the terms of any of the Credit
Documents, except as otherwise specifically set forth in this Agreement. The
Borrowers issue, ratify and confirm the representations, warranties and
covenants contained in the Credit Documents.

     14.  Modifications. This Agreement may not be supplemented, changed,
          -------------
waived, discharged, terminated, modified or amended, except by written
instrument executed by the parties.

     15.  Full Force and Effect. Except as expressly set forth above, the
          ---------------------
provisions of the Credit Agreement shall continue in full force and effect and
are hereby ratified and confirmed. A default under this Agreement shall be a
default under the Credit Agreement.

     IN WITNESS WHEREOF the parties hereto have signed and sealed this Agreement
on the day and year first above written.


                                        LENDER:

WITNESS:                                APPLIED BIOSCIENCE INTERNATIONAL INC.


 /s/ Joanne H. Teague                    By:  /s/ Fred B. Davenport, Jr.  (SEAL)
--------------------------                  ------------------------------
                                             Name:  Fred B, Davenport, Jr.
                                                  ------------------------     .
                                             Title: Vice President
                                                   -----------------------     .

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                                      BORROWERS:

                                      ENVIRON HOLDINGS, INC.,
                                      a Delaware corporation


 /s/ Joanne H. Teague                 By:   /s/ Joseph Highland          (SEAL)
--------------------------               --------------------------------
                                         Name:  Joseph Highland
                                              ---------------------------     .
                                         Title: Chairman, Chief Executive
                                                -------------------------
                                                Officer & Secretary
                                                -------------------------     .

                                      ENVIRON INTERNATIONAL CORPORATION,
                                      a Virginia corporation


 /s/ Joanne H. Teague                 By:   /s/ Joseph Highland          (SEAL)
--------------------------               --------------------------------
                                         Name:  Joseph Highland
                                              ---------------------------     .
                                         Title: Chairman, Chief Executive
                                                -------------------------
                                                Officer & Secretary
                                                -------------------------     .


                                      ENVIRON FACILITY SERVICES CORPORATION,
                                      a Virginia corporation


 /s/ Joanne H. Teague                 By:   /s/ Joseph Highland          (SEAL)
--------------------------               --------------------------------
                                         Name:  Joseph Highland
                                              ---------------------------     .
                                         Title: Chairman, Chief Executive
                                                -------------------------
                                                Officer & Secretary
                                                -------------------------     .



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