Document:

<PAGE>

                                                                   EXHIBIT 10.31

                                                                  EXECUTION COPY

                      AMENDMENT NO. 2 TO CREDIT AGREEMENT

     AMENDMENT dated as of March 24, 2000 to the Credit Agreement dated as of
February 5, 1997 (as heretofore amended, the "Credit Agreement") among TRIGON
HEALTHCARE, INC. (the "Borrower"), the BANKS party thereto (the "Banks") and
MORGAN GUARANTY TRUST COMPANY OF NEW YORK, as Agent (the "Agent").

     The parties hereto agree as follows:

     SECTION 1. Defined Terms; References. Unless otherwise specifically defined
herein, each term used herein which is defined in the Credit Agreement has the
meaning assigned to such term in the Credit Agreement. Each reference to
"hereof", "hereunder", "herein" and "hereby" and each similar reference and each
reference to "this Agreement" and each other similar reference contained in the
Credit Agreement shall, after this Amendment becomes effective, refer to the
Credit Agreement as amended hereby.

     SECTION 2. Amendment.  Clause (e) of Section 3.02 is amended by the
addition of the following proviso:

     ; provided that clause (e) shall not apply with respect to the
     representations and warranties set forth in Section 4.04(d) if and to the
     extent (i) the proceeds of such Borrowing are to be applied to pay maturing
     commercial paper substantially simultaneously with such Borrowing and (ii)
     such intended use of proceeds has been indicated in the applicable Notice
     of Borrowing.

     SECTION 3.  Representations of Borrower. The Borrower represents and
warrants that (i) the representations and warranties of the Borrower set forth
in Article 4 of the Credit Agreement will be true on and as of the Amendment
Effective Date and (ii) no Default will have occurred and be continuing on such
date.

     SECTION 4. Governing Law. This Amendment shall be governed by and construed
in accordance with the laws of the State of New York.

     SECTION 5. Counterparts.  This Amendment may be signed in any number of
counterparts, each of which shall be an original, with the same effect as if the
signatures thereto and hereto were upon the same instrument.

     SECTION 6. Effectiveness. This Amendment shall become effective on the date
(the "Amendment Effective Date") when the Agent shall have received from each of
the Borrower and the Required Banks a counterpart hereof signed by such party or
facsimile or other written confirmation (in form satisfactory to the Agent) that
such party has signed a counterpart hereof.

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed as of the date first above written.

                                TRIGON HEALTHCARE, INC.

                                By:_________________________
                                   Name:
                                   Title:
<PAGE>

                            MORGAN GUARANTY TRUST
                              COMPANY OF NEW YORK,
                             as Bank and as Agent

                            By:__________________________
                               Name:
                               Title:

                            THE BANK OF NEW YORK

                            By:___________________________
                               Name:
                               Title:

                            BANK ONE, NA (Main Office - Chicago)
                            (f/k/a The First National Bank of Chicago)

                            By:____________________________
                               Name:
                               Title:

                            THE FUJI BANK, LIMITED

                            By:____________________________
                               Name:
                               Title:

                            WACHOVIA BANK, N.A.
                            Formerly known as
                            WACHOVIA BANK OF NORTH
                             CAROLINA, N.A.

                            By:____________________________
                               Name:
                               Title:

                            THE ASAHI BANK, LTD.

                            By:___________________________
                               Name:
                               Title:

<PAGE>

                            CRESTAR BANK

                            By:__________________________
                               Name:
                               Title:

                            BANQUE NATIONALE DE PARIS

                            By:__________________________
                               Name:
                               Title:

                            By:____________________________
                               Name:
                               Title:

                            FIRST UNION NATIONAL BANK

                            By:___________________________
                               Name:
                               Title:

                            THE SANWA BANK, LIMITED

                            By:___________________________
                               Name:
                               Title:Exhibit 10.15

                           FIRST AMENDMENT TO LEASE
                            ------------------------

Reference  is made to a certain  Lease  dated  January 7, 2000,  by and  between
Thomas J. Teuten and John H. Spurr,  Jr., Trustees of 1050 Hingham Street Realty
Trust,  ("Landlord") and BioSphere,  Inc. ("Tenant") for Leased Premises located
at 1050 Hingham Street, Rockland, Massachusetts (the "Lease").

Now therefore, in consideration of these presents and other good and valuable
consideration, Landlord and Tenant agree that the Lease is hereby amended as
follows:

1.   The Leased  Premises  are  expanded  to include  certain  space next to the
     current Leased Premises, the "Expansion Space", as shown in Exhibit A-3.

2.   Rentable  Square Footage of the Leased  Premises set forth in the Reference
     Data Section is increased by the area of the Expansion Space,  5,198 square
     feet, making the total area approximately  12,995 square feet (being all of
     the Rentable  Square Footage on the First Floor of the Building)  effective
     on the Expansion Space Commencement Date, defined below.

3.   The Base  Rent set  forth in the  Reference  Data  Section  is  revised  to
     substitute  the  following  schedule  effective  on  the  "Expansion  Space
     Commencement  Date", which shall be the later to occur of (i) July 15, 2000
     or (ii) the date on which  Landlord's  Expansion  Construction  (defined in
     paragraph 7 of the First Amendment to Lease) is Substantially  Complete (as
     defined in Schedule A-1) but not later than  September 15, 2000, and in any
     event on the date on which  Tenant  occupies  any portion of the  Expansion
     Space for it's  purposes,  which  shall not include  entry for  purposes of
     preparing the Expansion Space for occupancy.
<TABLE>
<CAPTION>

                                                      Annual       Monthly
                  Period                               Rent          Rent
                  ------                               ----          ----
       <S>                                         <C>              <C>
       Expansion space
       commencement date to March 14, 2003         $ 270,296.00     $ 22,524.67

       March 15, 2003 to March 14, 2005            $ 276,143.75     $ 23,011.98
</TABLE>

4.   Electricity,  as set forth in Reference  Data Section,  shall be $11,825.00
     per year or $985.42 per month.

5.   Tenant's Proportionate Share: 32.675%

6.   Tenant  acknowledges  that Landlord has met its obligation  with respect to
     Landlord's Initial Construction and that Landlord has no further obligation
     therefor.
<PAGE>

7.   Landlord  agrees to perform work and make  installations  in the  Expansion
     Space as set  forth in  Schedule  A-1.  Such  work  and  installations  are
     referred  to as "  Landlord's  Expansion  Construction."  All of the terms,
     covenants and conditions of Schedule A-1 are  incorporated in this Lease by
     reference  and  shall be deemed a part of this  Lease as  though  fully set
     forth in the body of this Lease.

8.   Lease  Security:  Set forth in  Section 4 of the Lease is revised to be the
     schedule set forth in the Amended Reference Data Section.

9.   Tenant  agrees to disclose  to Landlord  from time to time during the Lease
     Term  financial  statements  or other credit  information  of Tenant at the
     request of Landlord upon reasonable advance notice. Landlord agrees to make
     reasonable  efforts to keep any such  financial  information  confidential,
     provided,  however,  that in connection  with bona fide  negotiation of the
     terms of  financing or sale of the  Building  with a specific,  prospective
     lender or  purchaser  (as opposed to any general  notice or  solicitation),
     Landlord may disclose such financial information  concerning Tenant to such
     prospective  financing entity or purchaser in confidence after prior notice
     in writing to Tenant.

10.  The capitalized terms contained herein shall have the same meaning as those
     terms contained in the Lease.

11.  Except as herein  expressly set forth, the Lease shall remain unchanged and
     is hereby ratified and remains in full force and effect.

         Executed under seal this 27th day of June, 2000.

                                                LANDLORD:
                                                1050 Hingham Street Realty Trust

                                                By: /s/ John H. Spurr, Jr.
                                                    ----------------------------
                                                    Trustee and not Individually

                                                TENANT:
                                                BioSphere, Inc.

                                                By: /s/ Robert M. Palladino
                                                    ----------------------------
                                                    duly authorized

<PAGE>

                                  SCHEDULE A-1

                        LANDLORD'S EXPANSION CONSTRUCTION

I. A. Landlord and Tenant have agreed upon a schematic plan (the "Schematic
Expansion Plan" Exhibit A-3) for construction of Landlord's Initial
Construction. On or prior to August 25, 2000, Landlord shall cause Landlord's
Architect to complete and deliver to Tenant a plan ("Tenant's Expansion Plan")
consistent with the Schematic Expansion Plan, for the construction of the Leased
Premises to prepare for Tenant's occupancy. Tenant's Expansion Plan shall
contain all details of Tenant's proposed improvements to the Leased Premises
which are required to permit such construction by Landlord, including, without
limitation, selections of wall coverings, selection of paint colors, selection
of carpeting, door keying schedule, and the heat factor, if any, of all
equipment intended to be used in, and the human load factor proposed for, each
room or other area. Tenant's Expansion Plan shall also include as many requests
for pricing of alternatives as Tenant wishes to consider prior to authorizing
Landlord to commence the work pursuant to Paragraph III below. All of the
improvements shown on Tenant's Expansion Plan as it is finally approved by
Landlord are hereinafter referred to as "Landlord's Expansion Construction."
Landlord shall allow Tenant and its agents and employees access to the Leased
Premises at all reasonable times from and after the date hereof for the purpose
of developing Tenant's Expansion Plan. Landlord agrees to reasonably cooperate
with Tenant and Tenant's agents, employees and contractors in all respects
during the development of Tenant's Expansion Plan. Tenant acknowledges that in
order to prepare Tenant's Expansion Plan, Landlord's Architect will need the
full cooperation of Tenant in making decisions with respect to such plan
concerning colors, carpets and other details described above. Tenant shall
approve Tenant's Expansion Plan within two (2) business days of receipt from
Landlord's Architect. Tenant agrees to act promptly and within the schedule set
forth by Landlord's Architect for the making of all decisions and approvals
required.

         B. Landlord has contracted with Landlord's Architect for all aspects of
Tenant's Expansion Plan which constitute a Building Standard installation as
defined in Schedule B. Subject to the Expansion Improvement Allowance defined in
Paragraph VIII below, the cost of the preparation of Tenant's Expansion Plan
shall be paid by Landlord. The foregoing is intended solely as a benefit to
Tenant based upon Landlord's contractual relationship with Landlord's Architect,
and Tenant shall have no obligation to utilize Landlord's Architect for the
preparation of Tenant's Expansion Plan.

         C. Tenant's Expansion Plan shall be subject to Landlord's approval,
which Landlord agrees not to unreasonably withhold or delay. In this connection,
any disapproval or withholding of approval of such Plan by Landlord shall not be
deemed unreasonable if the work designated on such Plan (i) is not in accordance
with the Building Standard or other standards adopted by Landlord consistent
with the terms and conditions of this Lease and timely communicated in advance

<PAGE>

to Tenant for construction in the Building, and with all applicable codes and
governmental regulations, including, without limitation, the energy conservation
provisions of the Massachusetts Building Code, (ii) will require the use of
contractors of a type other than those normally engaged by Landlord in the
construction of the Building without Landlord's prior approval, which shall not
be unreasonably withheld or delayed, (iii) will tend in Landlord's reasonable
judgment to delay completion of Landlord's Initial Construction (as shown on
such Plan) beyond the specified Commencement Date, (iv) is not practicable and
consistent with existing physical conditions in the Building and the plans for
the Building which have been filed with appropriate government authorities, (v)
will materially impair Landlord's ability to perform any of Landlord's
obligations under the Lease in the reasonable judgment of Landlord, (vi) will
adversely affect any portion of the Building other than the Leased Premises or
(vii) will exceed the capacity of the existing feeders or wiring installations
serving the Leased Premises.

II. Upon Landlord's approval of Tenant's Expansion Plan in accordance with
Paragraph I (C) above, Landlord will promptly negotiate a proposal from a
contractor acceptable to Landlord for Landlord's Expansion Construction as shown
on Tenant's Expansion Plan. The proposals submitted by the contractor shall be
submitted to Tenant for review forthwith after receipt with Landlord's
recommendation for contractor selection.

III. Tenant shall have two (2) business days in which to review such proposal,
and to approve the price therefor and to authorize Landlord to commence the
work. The price submitted by the contractor for all of Landlord's Expansion
Construction which is in excess of the Expansion Improvement Allowance (the
"Extra Work"), is hereinafter referred to as "Landlord's Extra Work Price." Any
failure by Tenant to authorize Landlord to perform any element of Landlord's
Expansion Construction within two (2) business days of submission to Tenant of
the material referred to above shall be deemed a Tenant delay within the meaning
of subparagraph C of Paragraph V of this Schedule A-1.

IV. Landlord agrees to construct Landlord's Expansion Construction at Landlord's
cost subject to the Expansion Improvement Allowance set forth below. The Extra
Work Price shall be borne by Tenant, and Landlord shall bill all or a portion of
the Extra Work Price to Tenant as work progresses. Tenant shall pay all amounts
due within ten (10) days. Such billings shall be based upon the ratio of the
Extra Work Price to the total cost of designing and constructing Landlord's
Expansion Construction.

V.       Completion of Landlord's Expansion Construction.

         A. Landlord's Expansion Construction shall be constructed in a good and
workmanlike manner with reasonable diligence, and shall constitute a single
non-recurring obligation on the part of Landlord. In the event this Lease is
renewed or extended for a further term by agreement or by operation of law, or
if Tenant shall exercise any option to lease or add additional rentable area to
the Leased Premises, Landlord's obligation to perform Landlord's Expansion
Construction shall not apply to any such renewal, extension or expansion.

<PAGE>

         B. In accordance with Section 3 of the Lease and paragraph 3 of the
First Amendment to Lease, unless it occurs prior to the Specified Commencement
Date, the date on which Substantial Completion of Landlord's Expansion
Construction occurs shall constitute the Expansion Space Commencement Date.
"Substantial Completion" of Landlord's Expansion Construction or words of
similar import shall mean completion of Landlord's Expansion Construction
exclusive of punch list items, i.e., details of construction, mechanical
adjustment and decoration, the completion of which will not materially interfere
with Tenant's use and occupancy of the Leased Premises for its normal business
purposes ("Punch List Items"), provided, however, that if such Substantial
Completion has been delayed on account of a Tenant Delay (defined below), then
Substantial Completion shall be deemed to have occurred on the date on which
Landlord reasonably determined Substantial Completion would have occurred but
for such Tenant Delay. The Punch List Items shall be determined by Landlord's
Architect during its final inspection of the Leased Premises during which
representatives of Landlord and Tenant shall be present. Landlord shall give
Tenant notice at least thirty (30) days in advance but not more than sixty (60)
days, of its reasonable estimate of the date upon which Landlord's Expansion
Construction will be substantially completed in order to permit Tenant to plan
and make reservations for installations and moving, provided, however, (i) such
notice shall only be a good faith estimate for the convenience of Tenant and
(ii) such notice shall not represent a warranty or representation to Tenant that
such substantial completion will have been achieved by the date specified in
such notice. At any reasonable time, after such Substantial Completion following
reasonable advance notice to Tenant, Landlord may enter the Leased Premises to
complete such Punch List Items. Landlord shall use reasonable diligence to
complete such Punch List Items within a reasonable time thereafter, and entry by
Landlord, its agents, servants, employees or contractors for such purpose shall
not constitute an actual or constructive eviction, in whole or in part, or
entitle Tenant to any abatement or diminution of rent, or relieve Tenant from
and of its obligations under this Lease, or impose any liability upon Landlord
or its agents by reason of inconvenience or annoyance to Tenant, or injury to or
interruption of Tenant's business, or otherwise.

         C. In the event Substantial Completion of Landlord's Expansion
Construction shall be delayed by reason of Tenant's delays in timely submission
of the Tenant's Expansion Plan, or approving any plans or specifications, or in
supplying information, or in approving estimates, or in giving authorizations
including, without limitation, authorization to proceed with the work, or by
reason of any changes by Tenant in any designations previously made by Tenant
pursuant to this Schedule, or by reason of any other acts or omissions of
Tenant, any such cause shall be referred to as "Tenant Delays."

         D. Tenant shall pay to Landlord within ten (10) days next following the
later of substantial completion of Landlord's Expansion Construction and the
rendition of a statement by Landlord to Tenant, that portion of Landlord's Extra
Work Price (as it may have been amended by agreement of Landlord and Tenant by
the addition of any additional extra work or otherwise).

VI. No Alterations (as opposed to Landlord's Expansion Construction) or

<PAGE>

installations of equipment or otherwise, whether or not constituting an
Alteration, shall be made or performed by or on behalf of Tenant in the
Expansion Space prior to the Expansion Space Commencement Date, without the
prior written approval of Landlord, which approval Landlord agrees not to
unreasonably withhold or delay provided either (i) such work does not impose any
additional burden on Landlord or Landlord's Contractor and does not materially
interfere with or delay completion of Landlord's Expansion Construction, in the
reasonable judgment of Landlord, or (ii) Tenant agrees to reimburse Landlord for
any reasonable cost of such additional burden and to treat any resulting delay
in Substantial Completion of Landlord's Expansion Construction as a Tenant
Delay. Any such sums billed to Tenant in connection with Alterations for
services provided by Landlord shall be payable by Tenant to Landlord, whether or
not the Lease Term shall have commenced, within ten (10) days next following the
rendition of a statement therefor by Landlord to Tenant.

VII. After the Expansion Space Commencement Date, and within ten (10) days next
following the request of Landlord, Tenant shall deliver to Landlord a written
statement executed and acknowledged by Tenant, in form reasonably satisfactory
to the holder of any mortgage of the Property, stating that (i) this Lease is
then in full force and effect and has not been modified (or, if modified,
setting forth the specific nature of all modifications), (ii) Tenant has
accepted the Leased Premises including the Expansion Space as constructed, (iii)
the Lease Term has commenced, and (iv) the rent payable under this Lease is
being paid by Tenant on a current basis with no offsets or counterclaims, or if
such is not the case, stating the correct facts and any reasons therefore if
applicable.

VIII. Expansion Improvement Allowance. Landlord shall be obligated to bear the
reasonable cost of designing and constructing Landlord's Expansion Construction
only up to the amount set forth in the Reference Data Section as "Expansion
Improvement Allowance." If the sum of the cost of design and Landlord's
Expansion Construction exceeds the amount of the Expansion Improvement
Allowance, Tenant shall be responsible for any excess to be billed as set forth
in Paragraphs IV and V above.

<PAGE>

                             AMENDED REFERENCE DATA
                           REFLECTING FIRST AMENDMENT

As used in this Lease, the following terms shall have the respective meanings
set forth below except when and to the extent reference is made to particular
Sections of the Lease:

Date of Lease:                     January 7, 2000

Date of Amendments:                First Amendment June 27, 2000

Landlord:                          Thomas J. Teuten and John H. Spurr, Jr.,
                                   Trustees of 1050 Hingham Street Realty Trust.

Landlord's Address:                20 Winthrop Square, Boston, Massachusetts
                                   02110-1229.

Tenant:                            BioSphere, Inc., a Delaware Corporation.

Tenant's Address:                  1050 Hingham Street
                                   Rockland, Massachusetts 02370

Property:                          Landlord's  land and  improvements  thereon
                                   known as 1050 Hingham Street,  Rockland,
                                   Massachusetts 02370.

Building:                          The three-story building located on the
                                   Property.

Leased Premises:                   The entire first floor (excluding the common
                                   entrance lobby) of the Building as shown on
                                   Exhibits A-2 and A-3.

Rentable Square Footage
of the Leased Premises:            Prior to First Amendment 7,797 square foot.
                                   After First Amendment 12,995 square feet.

Total Rentable Square
Footage of the Building:           39,771 square feet.

Use of Leased Premises:            Administrative offices for a medical device
                                   company and ancillary uses related thereto
                                   including research and development and light
                                   manufacturing to the extent described in
                                   Exhibit D attached hereto and incorporated
                                   herein, provided that such research and
                                   development involve no hazardous materials,
                                   solid waste, noise or fumes beyond the Leased
                                   Premises or any impact on the Building, its
                                   operations or the operations of other tenants
                                   in the Building.
<PAGE>

                             AMENDED REFERENCE DATA
                           Reflecting FIrst Amendment

Lease Term:                   Five (5) years

Specified Commencement
Date:                         March 15, 2000

Commencement Date:            The Specified  Commencement  Date or such other
                              date as is determined in accordance with the
                              terms of Section 3.

Expansion Space
Commencement Date:            July 15, 2000 or such other date as is determined
                              under Paragraph 3 of the First Amendment.

Expansion Improvement
Allowance:                    Up to $93,564.

Base Rent:
                                              Annual              Monthly
Periods                                      Base Rent          Installment
-------                                      ---------          -----------
March 15, 2000 to July 14, 2000            $ 155,940.00         $ 12,995.00
July 15, 2000 to February 14, 2003         $ 270,296.00         $ 22,524.67
February 15, 2003-February 14, 2005        $ 276,143.75         $ 23,011.98

LeaseSecurity:                An irrevocable letter of credit (the "Letter of
                              of Credit") or cash Security Deposit of $140,000
                              at the Commencement  Date and $234,000  after the
                              execution of the First Amendment,  to be reduced
                              as scheduled below, subject to Section 4.

                              Period                                     Amount
                              ------                                     ------
                              3/15/00 - First Amendment Execution      $ 140,000
                              First Amendment Execution - 3/14/01      $ 234,000
                              3/15/01 - 3/14/02                        $ 198,000
                              3/15/02 - 3/14/03                        $ 157,800
                              3/15/03 - 3/14/04                        $ 110,500
                              3/15/04 - 3/31/05                         $ 58,000

Base Operating Costs:         Operating  costs for the  calendar  year  2000,
                              grossed up to reflect  100%  occupancy  for a full
                              calendar year.

Base Taxes:                   Taxes for the fiscal year ended June 30, 1999.
<PAGE>

                             AMENDED REFERENCE DATA
                           REFLECTING FIRST AMENDMENT

Electricity:                  Prior to First Amendment $6,627.45 per year or
                              $552.29 per month.  After First Amendment
                              $11, 825.00 per year or $985.42 per month.

Tenant's Proportionate
Share:                        Prior to First Amendment 19.605%.  After First
                              Amendment 32.675%.

Broker:                       Meredith & Grew, Incorporated.

Insurance:                    $1,000,000/$3,000,000 per occurrence public
                              liability; $1,000,000 per occurrence property
                              damage. Personal Property insurance for all risks
                              to full insurable value of personalty in the
                              Leased Premises.

Landlord's Initial
Construction:                 Landlord shall provide a buildout subject to the
                              conditions of Schedule A and Tenant Construction
                              Contribution of up to $31,188 toward the cost of
                              design and construction of Landlord's Initial
                              Construction to the extent such cost exceeds
                              $140,346.

Landlord's Expansion
Construction:                 Landlord  shall  provide a buildout for the
                              Expansion Space subject to the  conditions of
                              Schedule A-1 with Landlord's cost of design and
                              construction limited to the Expansion Improvement
                              Allowance.

<PAGE>
                                  EXHIBIT A-3

                     [DEPICTION OF SCHEMATIC EXPANSION PLAN]

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