Document:

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                                                                    Exhibit 10.8

[METOBOLIX LOGO]                         21 Erie Street
WHERE NATURE PERFORMS(TM)                Cambridge, Massachusetts 02139-4260 USA
                                         Tel: 617.492.0505 - Fax: 617-492-1996
                                         Web: www.metabolix.com

                                   September 18, 2006

James J. Barber
c/o Metabolix, Inc.
21 Erie Street
Cambridge, MA  02139

     Re:  AMENDED AND RESTATED EMPLOYMENT AGREEMENT

Dear Jim:

     This letter is to confirm our understanding with respect to your employment
by Metabolix, Inc. (the "Company"). The terms and conditions agreed to in this
letter are hereinafter referred to as the "Agreement". In consideration of the
mutual promises and covenants contained in this Agreement, and for other good
and valuable consideration, the receipt and sufficiency of which are hereby
mutually acknowledged, we have agreed as follows:

     1.   EMPLOYMENT.

          (a)  GENERAL. The Company will employ you, and you will be employed by
     the Company, as the President and Chief Executive Officer of the Company,
     reporting to and serving on the Board of Directors (the "Board"), and you
     shall have the responsibilities, duty and authority commensurate with that
     position. You will also perform such other and/or different services for
     the Company as may be assigned to you from time to time by the Board. You
     agree that if your employment hereunder ends for any reason, you will
     tender your resignation to the Board.

          (b)  DEVOTION TO DUTIES. While you are employed hereunder, you will
     use your best efforts, skills and abilities to perform faithfully all
     duties assigned to you pursuant to this Agreement and will devote your full
     business time and energies to the business and affairs of the Company.
     While you are employed hereunder, you will not undertake any other
     employment from any person or entity without the prior written consent of
     the Company.

     2.   EMPLOYMENT AT WILL. Your employment hereunder will be on an "at-will"
basis and may be terminated by the Company or by you at any time for any reason
or for no reason.

     3.   COMPENSATION.

          (a)  BASE SALARY. While you are employed hereunder, the Company will
     pay you a base salary at the annual rate of $19,583.00 per month
     (annualized at $235,000.00) (the "Base Salary"). This Base Salary is
     effective January 1, 2005, and may be subject to

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James J. Barber
September 18, 2006
Page 2

     upward (but not downward) adjustment from time to time in the discretion of
     the Company and will be adjusted higher by the Board to levels comparable
     for similar companies as determined by the Board in its sole discretion in
     the event that there is a public offering. The Company will deduct from
     each monthly salary payment all amounts required to be deducted or withheld
     under applicable law or under any employee benefit plan in which you
     participate.

          (b)  BONUSES. In addition to the foregoing, the Company on or before
     December 31, 2006, will establish a formalized bonus scheme and pay you an
     annual bonus (a "Bonus") in an amount to be determined by the Company's
     Compensation Committee. The amount will be based on several criteria,
     including the financial condition of the Company and its overall
     performance for the year, but will be strongly influenced by your
     contributions toward the achievement of established corporate goals and
     objectives, as well as other contributions that add recognizable value to
     the Company. The present target for executive bonuses is 50% of Base Salary
     (the "Target Bonus"). This Target Bonus will be subject to revision from
     time to time by the Compensation Committee. In order to receive an annual
     bonus, you must be employed at the time of a timely payment, which will be
     paid on or before March 15 of the year following the year in which it is
     earned.

          (c)  EQUITY COMPENSATION. The Company has granted to you pursuant to
     the Metabolix, Inc. 2005 Stock Plan the following Options:1/

               (i)    Grant of 243,235 incentive stock options at the exercise
          price of $1.50, the fair market value at the date of grant. 44,000 of
          such shares shall vest as of the grant date. Subject to your continued
          employment and Section 4 of this Agreement, the remainder will vest in
          equal increments on a quarterly basis over a four year period as
          though vesting had begun on January 1, 2005.

               (ii)   Grant of 51,333 options at the exercise price of $1.50,
          the fair market value at the date of grant. Vesting of this option
          shall occur only if:

                      (A)   the Company, prior to June 30, 2006: (I) completes
               an initial public offering with proceeds of at least $40 million
               and a price per share of at least $8.00 (an "IPO"), or (II) signs
               a definitive agreement for the merger or sale of the Company that
               provides for liquidity in the form of cash or readily-marketable
               securities in exchange for all of the Company's outstanding
               shares, provided that in the event the IPO is delayed by the
               Company's Board of Directors so that it can negotiate a merger or
               sale of the Company, the Board will make an appropriate extension
               of such date; and

----------
(1)  Options granted prior to the execution of this Agreement and not identified
here shall continue to vest in accordance with their terms.

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James J. Barber
September 18, 2006
Page 3

                      (B)   in the period prior to the occurrence of such
               contingency event the Company has not raised capital: (I) through
               a sale of shares on terms that are less favorable to the Company
               than the terms of the 2004 offering, or (II) through an offering
               solely to existing investors.

          The foregoing conditions were not met and, accordingly, the options
          described in this clause (ii) have expired.

               (iii)  Grant of 51,333 options at the exercise price of $1.50,
          fair market value at the date of grant. Vesting of this option shall
          occur only if

                      (A)   the Company, prior to December 31, 2007: (I)
               completes an IPO, or (II) signs a definitive agreement for the
               merger or sale of the Company that provides for liquidity in the
               form of cash or readily-marketable securities in exchange for all
               of the Company's outstanding shares, and

                      (B)   in the period prior to the occurrence of such
               contingency event the Company has not raised capital: (I) through
               a sale of shares on terms that are less favorable to the Company
               than the terms of the 2004 offering, or (II) through an offering
               solely to existing investors.

          For avoidance of doubt, if the option described in Section 3(c)(ii)
          above vests, this option shall vest as well. If vesting occurs, it
          shall occur as follows: 50% of such shares will vest upon occurrence
          of the contingency event, and, subject to your continued employment
          and Section 4 of this Agreement, the remainder will vest in equal
          increments on a quarterly basis over a four year period as if the
          vesting had commenced January 1, 2005.

               (iv)   Grant of 51,334 options at the exercise price of $1.50,
          the fair market value at the time of grant. Vesting of this option
          shall occur only if

                      (A)   ADM Polymer Corporation, or an affiliate, exercises
               the Option as defined in the Technology Alliance and Option
               Agreement by and between ADM Polymer Corporation and Metabolix,
               Inc., and

                      (B)   in the period prior to the occurrence of such
               contingency event the Company has not raised capital: (I) through
               a sale of shares on terms that are less favorable to the Company
               than the terms of the 2004 offering, or (II) through an offering
               solely to existing investors.

          If vesting occurs, it shall occur as follows: 50% of such shares will
          vest upon occurrence of the contingency event, and, subject to your
          continued employment and Section 4 of this Agreement, the remainder
          will vest in equal increments on a

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James J. Barber
September 18, 2006
Page 4

          quarterly basis over a four year period as if the vesting had
          commenced January 1, 2005.

          The parties acknowledge and agree that the foregoing contingency event
          has occurred.

               (v)    The Company, in the Board's sole discretion, may from time
     to time grant to you stock options, restricted stock or other forms of
     equity compensation pursuant to the Metabolix, Inc. 2005 Stock Plan or any
     other authorized stock plan in effect at the time.

          (d)  VACATION. You will be entitled to paid vacation and paid
     holidays, accrued and used in accordance with the Company's policies as
     currently in effect. All vacation days will be taken at times mutually
     agreed by you and the Company and will be subject to the business needs of
     the Company.

          (e)  FRINGE BENEFITS. You will be entitled to participate in employee
     benefit plans which the Company provides or may establish for the benefit
     of its senior executives generally (for example, group life, disability,
     medical, dental and other insurance, retirement, pension, profit-sharing
     and similar plans) (collectively, the "Fringe Benefits"). Your eligibility
     to participate in the Fringe Benefits and receive benefits thereunder will
     be subject to the plan documents governing such Fringe Benefits. Nothing
     contained herein will require the Company to establish or maintain any
     Fringe Benefits.

          (f)  LOAN FORGIVENESS. Pursuant to your prior employment agreement
     with the Company dated November 28, 1999, the Company provided you with a
     loan of $75,000. In exchange for your covenants hereunder, the Company has
     forgiven that loan, effective as of December 14, 2005.

     4.   TERMINATION.

          (a)  GENERAL. As an at-will employee, your employment may be
     terminated at any time for any reason or for no reason. Upon termination,
     unless otherwise specifically provided herein, you shall be eligible only
     to receive (i) the portion of your Base Salary as has accrued prior to such
     termination and has not yet been paid, (ii) an amount equal to the value of
     your accrued unused vacation days, and (iii) reimbursement for expenses
     properly incurred by you on behalf of the Company prior to such termination
     if such expenses are properly documented in accordance with Company policy
     and practice and submitted for reimbursement within thirty (30) days of the
     termination date (collectively, the "Accrued Obligations"). Such amounts
     will be paid promptly after termination in accordance with applicable law.

          (b)  TERMINATION WITHOUT CAUSE OR WITH GOOD REASON. Except as provided
     in Section 4(c) hereof, in the event that your employment is terminated by
     the Company without Cause or by you with Good Reason (each, as defined
     below), in addition to the

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James J. Barber
September 18, 2006
Page 5

     Accrued Obligations, and contingent on your provision of a timely and
     complete release of claims against the Company, you shall be entitled to
     receive continuation of your Base Salary in effect at the time of
     termination for the period of twelve (12) months following the termination.
     To the extent required by Section 409A of the Internal Revenue Code of
     1986, as amended (the "Code"), the first installment of such Base Salary in
     the amount of six (6) months' Base Salary shall be payable on the first
     business day following the six (6) month anniversary of the effective date
     of termination, and the remainder shall be payable in accordance with the
     Company's regular payroll procedures thereafter. If Section 409A of the
     Code is not then applicable, such Base Salary continuation shall commence
     immediately from the date of termination. In addition, should the award of
     a Bonus have become customary, you shall be entitled to a payment equal to
     the average of the Bonuses paid to you (if any) in the two years preceding
     the termination, to be paid (A) on the first business day following the six
     (6) month anniversary of the effective date of termination, to the extent
     required by Section 409A of the Code, or (B) if Section 409A of the Code is
     not then applicable, within thirty (30) days following the termination. In
     addition to the foregoing, you shall be entitled to receive payment of
     COBRA premiums to maintain medical and dental benefits, if any, in effect
     at the time of termination for the period of twelve (12) months following
     the termination.

          (c)  TERMINATION WITHOUT CAUSE OR WITH GOOD REASON BEFORE OR AFTER A
     CHANGE OF CONTROL.

               (i)    In the event that your employment is terminated by the
     Company without Cause or by you for Good Reason (each, as defined below)
     within the twenty-four (24) month period immediately following or the two
     month period immediately prior to a Change of Control (as defined below),
     in addition to the Accrued Obligations, and contingent on your provision of
     a timely release of claims against the Company, you shall be entitled to
     receive:

                      (A)   continuation of your Base Salary in effect at the
     time of termination for the period of twelve (12) months following the
     termination. To the extent required by Section 409A of the Code, the first
     installment of such Base Salary in the amount of six (6) months' Base
     Salary shall be payable on the first business day following the six (6)
     month anniversary of the effective date of termination, and the remainder
     shall be payable in accordance with the Company's regular payroll
     procedures thereafter. If Section 409A of the Code is not then applicable,
     such Base Salary continuation shall commence immediately from the date of
     termination.

                      (B)   In addition, should the award of a Bonus have become
     customary, you shall be entitled to a payment equal to the average of the
     Bonuses paid to you (if any) in the two years preceding the termination, to
     be paid (A) on the first business day following the six (6) month
     anniversary of the effective date of termination, to the extent required by
     Section 409A of the Code, or (B) if Section 409A of the Code is not then
     applicable, within thirty (30) days following the termination.

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James J. Barber
September 18, 2006
Page 6

                      (C)   continued payment of COBRA premiums to maintain
     medical and dental benefits, if any, in effect at the time of termination
     for the period of twelve (12) months following the termination; and

                      (D)   full vesting of all options and restricted stock
     granted to you under the Metabolix Inc. 1995 Stock Plan, the Metabolix Inc.
     2005 Stock Plan or any authorized successor stock plan provided that the
     conditions to vesting other than the passage of time have been satisfied.

               (ii)   You agree that the payments and benefits hereunder, and
     under all other contracts, arrangements or programs that apply to you (the
     "Company Payments"), shall be reduced to an amount that is one dollar less
     than the amount that would trigger an excise tax under Section 4999 of the
     Code, as determined in good faith by the Company's independent public
     accountants, PROVIDED, HOWEVER, that the reduction shall occur only if the
     reduced Company Payments received by you (after taking into account further
     reductions for applicable federal, state and local income, social security
     and other taxes) would be greater than the unreduced Company Payments to be
     received by you minus (i) the excise tax payable with respect to such
     Company Payments under Section 4999 of the Code; and (ii) all applicable
     federal, state and local income, social security and other taxes on such
     Company Payments. You and the Company agree to cooperate in good faith with
     each other in connection with any administrative or judicial proceedings
     concerning the existence or amount of golden parachute penalties with
     respect to payments or benefits that you receive.

          (d)  "CAUSE". As used herein, "Cause" shall be defined as (i) your
     conviction for, or plea of nolo contendere, to a felony or a crime
     involving moral turpitude, (ii) your commission of a material act of
     personal dishonesty or a breach of fiduciary duty involving personal profit
     in connection with your employment by the Company, (iii) your commission of
     an act which the Board of Directors shall reasonably have found to have
     involved willful misconduct or gross negligence on your part in the conduct
     of your duties under this Agreement, (iv) your habitual absenteeism, (v)
     your material breach of any material provision of this Agreement continuing
     for thirty days after your receipt of written notice thereof from the
     Company, or (vi) the willful and continued failure by you to perform
     substantially your duties with the Company (other than any such failure
     resulting from your incapacity due to physical or mental illness).

          (e)  "CHANGE OF CONTROL". As used herein, a "Change of Control" shall
     occur or be deemed to have occurred only upon any one or more of the
     following events:

               (i)    a merger or consolidation of the Company other than a
          merger or consolidation which would result in the voting securities of
          the Company outstanding immediately prior thereto continuing to
          represent (either by remaining outstanding or by being converted into
          voting securities of the surviving entity or the parent of such
          corporation) at least fifty percent (50%) of

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James J. Barber
September 18, 2006
Page 7

          the total voting power represented by the voting securities of the
          Company or such surviving entity or parent of such corporation
          outstanding immediately after such merger or consolidation;

               (ii)   the sale or disposition by the Company of all or
          substantially all of the Company' s assets; or

               (iii)  any one person, entity or group, who is not a shareholder
          at time of execution of this Agreement, acquires ownership of capital
          stock of the Company that, together with the capital stock of the
          Company already held by such person, entity or group, constitutes more
          than 50% of the total fair market value or total voting power of the
          capital stock of the Company; provided, however, if any one person,
          entity or group is considered to own more than 50% of the total fair
          market value or total voting power of the capital stock of the
          Company, the acquisition of additional capital stock by the same
          person, entity or group shall not be deemed to be a Change of Control,
          and further provided that the foregoing shall not be deemed a Change
          of Control if the average stock price paid for each share of stock
          held by the person, entity or group is less than $8.00/share (provided
          that such price shall be adjusted as appropriate to reflect any stock
          dividend, stock split, or recapitalization of the Company after the
          date of this agreement).

          (f)  "Good Reason" shall be defined as, in the absence of a cure by
     the Company within 30 days after written notice by you to the Board, a (i)
     a change in title of President and Chief Executive Officer, (ii) a material
     diminution of responsibilities, duties or powers, (iii) a reduction in Base
     Salary, Target Bonus, vacation or other benefits, except that benefits need
     only be substantially equivalent, or (iv) a requirement that you relocate
     your principal place of employment to (or that you travel more than 50 days
     in any calendar year to the Company's principal place of business in) a
     location more than 50 miles from its current location in Cambridge,
     Massachusetts, PROVIDED THAT you must provide the Company with at least
     thirty (30) days advance written notice of your intent to terminate your
     employment hereunder and an opportunity to cure.

     5.   NONCOMPETITION, NONDISCLOSURE AND INVENTIONS OBLIGATIONS. Your
Employee Noncompetition, Nondisclosure and Inventions Agreement dated November
28, 1999, shall continue in full force and effect in accordance with its terms.

     6.   DISCLOSURE TO FUTURE EMPLOYERS. You will provide, and the Company, in
its discretion, may similarly provide, a copy of the covenants contained in The
Employee Noncompetition, Nondisclosure and Inventions Agreement to any business
or enterprise which you may, directly or indirectly, own, manage, operate,
finance, join, control or in which you may participate in the ownership,
management, operation, financing, or control, or with which you may be connected
as an officer, director, employee, partner, principal, agent, representative,
consultant or otherwise.

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James J. Barber
September 18, 2006
Page 8

     7.   REPRESENTATIONS. You hereby represent and warrant to the Company that
you understand this Agreement, that you enter into this Agreement voluntarily
and that your employment under this Agreement will not conflict with any legal
duty owed by you to any other party.

     8.   GENERAL.

          (a)  NOTICES. All notices, requests, consents and other communications
     hereunder which are required to be provided, or which the sender elects to
     provide, in writing, will be addressed to the receiving party's address set
     forth above or to such other address as a party may designate by notice
     hereunder, and will be either (i) delivered by hand, (ii) sent by overnight
     courier, or (iii) sent by registered or certified mail, return receipt
     requested, postage prepaid. All notices, requests, consents and other
     communications hereunder will be deemed to have been given either (i) if by
     hand, at the time of the delivery thereof to the receiving party at the
     address of such party set forth above, (ii) if sent by overnight courier,
     on the next business day following the day such notice is delivered to the
     courier service, or (iii) if sent by registered or certified mail, on the
     fifth business day following the day such mailing is made.

          (b)  ENTIRE AGREEMENT. This Agreement, together with any Stock Option
     Agreements executed by you and the Company (either prior to or in
     conjunction with this Agreement), the Employee Noncompetition,
     Nondisclosure and Inventions Agreement and the other agreements
     specifically referred to herein, embodies the entire agreement and
     understanding between the parties hereto with respect to the subject matter
     hereof and supersedes all prior oral or written agreements and
     understandings relating to the subject matter hereof, including without
     limitation the Employment Agreement between you and the Company dated
     December 14, 2005. No statement, representation, warranty, covenant or
     agreement of any kind not expressly set forth in this Agreement will
     affect, or be used to interpret, change or restrict, the express terms and
     provisions of this Agreement.

          (c)  MODIFICATIONS AND AMENDMENTS. The terms and provisions of this
     Agreement may be modified or amended only by written agreement executed by
     the parties hereto.

          (d)  WAIVERS AND CONSENTS. The terms and provisions of this Agreement
     may be waived, or consent for the departure therefrom granted, only by
     written document executed by the party entitled to the benefits of such
     terms or provisions. No such waiver or consent will be deemed to be or will
     constitute a waiver or consent with respect to any other terms or
     provisions of this Agreement, whether or not similar. Each such waiver or
     consent will be effective only in the specific instance and for the purpose
     for which it was given, and will not constitute a continuing waiver or
     consent.

          (e)  ASSIGNMENT. The Company may assign its rights and obligations
     hereunder to any person or entity that succeeds to all or substantially all
     of the Company's business or that aspect of the Company's business in which
     you are principally involved or to any

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James J. Barber
September 18, 2006
Page 9

     Company Affiliate. You may not assign your rights and obligations under
     this Agreement without the prior written consent of the Company and any
     such attempted assignment by you without the prior written consent of the
     Company will be void.

          (f)  GOVERNING LAW. This Agreement and the rights and obligations of
     the parties hereunder will be construed in accordance with and governed by
     the law of Massachusetts, without giving effect to the conflict of law
     principles thereof.

          (g)  JURISDICTION, VENUE AND SERVICE OF PROCESS. Any legal action or
     proceeding with respect to this Agreement will be brought in the courts of
     Massachusetts or of the United States of America for THE District of
     Massachusetts. By execution and delivery of this Agreement, each of the
     parties hereto accepts for itself and in respect of its property, generally
     and unconditionally, the exclusive jurisdiction of the aforesaid courts.

          (h)  SEVERABILITY. The parties intend this Agreement to be enforced as
     written. However, if any portion or provision of this Agreement is to any
     extent declared illegal or unenforceable by a duly authorized court having
     jurisdiction, then the remainder of this Agreement, or the application of
     such portion or provision in circumstances other than those as to which it
     is so declared illegal or unenforceable, will not be affected thereby, and
     each portion and provision of this Agreement will be valid and enforceable
     to the fullest extent permitted by law.

          (i)  HEADINGS AND CAPTIONS. The headings and captions of the various
     subdivisions of this Agreement are for convenience of reference only and
     will in no way modify or affect the meaning or construction of any of the
     terms or provisions hereof.

          (j)  ACKNOWLEDGMENTS. You hereby acknowledge and recognize that the
     enforcement of any of the provisions in this Agreement and the
     Noncompetition, Nondisclosure and Inventions Agreement may potentially
     interfere with your ability to pursue a proper livelihood. You represent
     that you are knowledgeable about the business of the Company and further
     represent that you are capable of pursuing a career in other industries
     other than the field of noncompetition as set forth in the Noncompetition,
     Nondisclosure and Inventions Agreement to earn a proper livelihood. You
     recognize and agree that the enforcement of the Noncompetition,
     Nondisclosure and Inventions Agreement is necessary to ensure the
     preservation, protection and continuity of the business, trade secrets and
     goodwill of the Company. You agree that, due to the proprietary nature of
     the Company's business, the restrictions set forth in the Noncompetition,
     Nondisclosure and Inventions Agreement are reasonable as to time and scope.

          (k)  TAXES. All payments required to be made by the Company to you
     under this Agreement shall be subject to the withholding of such amounts
     for taxes and other payroll deductions as the Company may reasonably
     determine it should withhold pursuant to any applicable law or regulation.
     To the extent applicable, it is intended that this Agreement comply with
     the provisions of Section 409A of the Code, and this Agreement shall be
     construed and applied in a manner consistent with this intent. In the

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James J. Barber
September 18, 2006
Page 10

     event that any severance payments or benefits hereunder are determined by
     the Company to be in the nature of nonqualified deferred compensation
     payments, you and the Company hereby agree to take such actions as may be
     mutually agreed to ensure that such payments or benefits comply with the
     applicable provisions of Section 409A of the Code and the official guidance
     issued thereunder. Notwithstanding the foregoing, the Company does not
     guarantee the tax treatment or tax consequences associated with any payment
     or benefit arising under this Agreement.

          (l)  COUNTERPARTS. This Agreement may be executed in two or more
     counterparts, and by different parties hereto on separate counterparts,
     each of which will be deemed an original, but all of which together will
     constitute one and the same instrument.

     If the foregoing accurately sets forth our agreement, please so indicate by
signing and returning to us the enclosed copy of this Agreement.

                                         Very truly yours,

                                         Metabolix, Inc.

                                         By:. /s/ Thomas G. Auchincloss, Jr.
                                             -----------------------------------
                                         Name: Thomas G. Auchincloss, Jr.
                                         Title: CFO

ACCEPTED AND APPROVED:

/s/ James J. Barber                       9/19/06
----------------------------             -------------
James J. Barber                          Date<Page>

                                                                    Exhibit 10.9

[METABOLIX LOGO]                         21 Erie Street
WHERE NATURE PERFORMS(TM)                Cambridge, Massachusetts 02139-4260 USA
                                         Tel: 617.492.0505 - Fax: 617-492-1996
                                         Web: www.metabolix.com

                                  September 18, 2006

Thomas G. Auchincloss, Jr.
c/o Metabolix, Inc.
21 Erie Street
Cambridge, MA  02139

     Re: AMENDED AND RESTATED EMPLOYMENT AGREEMENT

Dear Tom:

     This letter is to confirm our understanding with respect to your employment
by Metabolix, Inc. (the "Company"). The terms and conditions agreed to in this
letter are hereinafter referred to as the "Agreement". This Agreement amends and
restates your Employment Agreement dated January 10, 2006. In consideration of
the mutual promises and covenants contained in this Agreement, and for other
good and valuable consideration, the receipt and sufficiency of which are hereby
mutually acknowledged, we have agreed as follows:

     1.   EMPLOYMENT.

          (a)  GENERAL. The Company will employ you, and you will be employed by
     the Company, as the Chief Financial Officer and Vice President, Finance and
     Corporate Development of the Company, reporting to the Chief Executive
     Officer, and you shall have the responsibilities, duty and authority
     commensurate with that position. You will also perform such other and/or
     different services for the Company as may be assigned to you from time to
     time. You agree that if your employment hereunder ends for any reason, you
     will tender your resignation to the Company.

          (b)  DEVOTION TO DUTIES. While you are employed hereunder, you will
     use your best efforts, skills and abilities to perform faithfully all
     duties assigned to you pursuant to this Agreement and will devote your full
     business time and energies to the business and affairs of the Company.
     While you are employed hereunder, you will not undertake any other
     employment from any person or entity without the prior written consent of
     the Company.

     2.   EMPLOYMENT AT WILL. Your employment hereunder will be on an "at-will"
basis and may be terminated by the Company or by you at any time for any reason
or for no reason.

     3.   COMPENSATION.

          (a)  BASE SALARY. While you are employed hereunder, the Company will
     pay you a base salary at the annual rate of $16,666.66 per month
     (annualized at $200,000.00) (the

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Thomas G. Auchincloss, Jr.
September 18, 2006
Page 2

     "Base Salary"). This Base Salary is effective July 1, 2006, and may be
     subject to upward (but not downward) adjustment from time to time in the
     discretion of the Company. The Company will deduct from each monthly salary
     payment all amounts required to be deducted or withheld under applicable
     law or under any employee benefit plan in which you participate.

          (b)  BONUSES. In addition to the foregoing, the Company on or before
     December 31, 2006, will establish a formalized bonus scheme and pay you an
     annual bonus (a "Bonus") in an amount to be determined by the Company's
     Compensation Committee. The amount will be based on several criteria,
     including the financial condition of the Company and its overall
     performance for the year, but will be strongly influenced by your
     contributions toward the achievement of established corporate goals and
     objectives, as well as other contributions that add recognizable value to
     the Company. The present target for executive bonuses is 50% of Base Salary
     (the "Target Bonus"). This Target Bonus will be subject to revision from
     time to time by the Compensation Committee. In order to receive an annual
     bonus, you must be employed at the time of a timely payment, which will be
     paid on or before March 15 of the year following the year in which it is
     earned.

          (c)  EQUITY COMPENSATION. The Company, in the Board's sole discretion,
     may from time to time grant to you stock options, restricted stock or other
     forms of equity compensation pursuant to the Metabolix, Inc. 2005 Stock
     Plan or any other authorized stock plan in effect at the time.

          (d)  VACATION. You will be entitled to paid vacation and paid
     holidays, accrued and used in accordance with the Company's policies as
     currently in effect. All vacation days will be taken at times mutually
     agreed by you and the Company and will be subject to the business needs of
     the Company.

          (e)  FRINGE BENEFITS. You will be entitled to participate in employee
     benefit plans which the Company provides or may establish for the benefit
     of its senior executives generally (for example, group life, disability,
     medical, dental and other insurance, retirement, pension, profit-sharing
     and similar plans) (collectively, the "Fringe Benefits"). Your eligibility
     to participate in the Fringe Benefits and receive benefits thereunder will
     be subject to the plan documents governing such Fringe Benefits. Nothing
     contained herein will require the Company to establish or maintain any
     Fringe Benefits.

     4.   TERMINATION.

          (a)  GENERAL. As an at-will employee, your employment may be
     terminated at any time for any reason or for no reason. Upon termination,
     unless otherwise specifically provided herein, you shall be eligible only
     to receive (i) the portion of your Base Salary as has accrued prior to such
     termination and has not yet been paid, (ii) an amount equal to the value of
     your accrued unused vacation days, and (iii) reimbursement for expenses
     properly incurred by you on behalf of the Company prior to such termination
     if such expenses are properly documented in accordance with Company policy
     and practice and submitted for

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Thomas G. Auchincloss, Jr.
September 18, 2006
Page 3

     reimbursement within thirty (30) days of the termination date
     (collectively, the "Accrued Obligations"). Such amounts will be paid
     promptly after termination in accordance with applicable law.

          (b)  TERMINATION WITHOUT CAUSE OR WITH GOOD REASON. Except as provided
     in Section 4(c) hereof, in the event that your employment is terminated by
     the Company without Cause or by you with Good Reason (each, as defined
     below), in addition to the Accrued Obligations, and contingent on your
     provision of a timely and complete release of claims against the Company,
     you shall be entitled to receive continuation of your Base Salary in effect
     at the time of termination for the period of twelve (12) months following
     the termination. To the extent required by Section 409A of the Internal
     Revenue Code of 1986, as amended (the "Code"), the first installment of
     such Base Salary in the amount of six (6) months' Base Salary shall be
     payable on the first business day following the six (6) month anniversary
     of the effective date of termination, and the remainder shall be payable in
     accordance with the Company's regular payroll procedures thereafter. If
     Section 409A of the Code is not then applicable, such Base Salary
     continuation shall commence immediately from the date of termination. In
     addition, should the award of a Bonus have become customary, you shall be
     entitled to a payment equal to the average of the Bonuses paid to you (if
     any) in the two years preceding the termination, to be paid (A) on the
     first business day following the six (6) month anniversary of the effective
     date of termination, to the extent required by Section 409A of the Code, or
     (B) if Section 409A of the Code is not then applicable, within thirty (30)
     days following the termination. In addition to the foregoing, you shall be
     entitled to receive payment of COBRA premiums to maintain medical and
     dental benefits, if any, in effect at the time of termination for the
     period of twelve (12) months following the termination.

          (c)  TERMINATION WITHOUT CAUSE OR WITH GOOD REASON BEFORE OR AFTER A
     CHANGE OF CONTROL.

               (i)    In the event that your employment is terminated by the
     Company without Cause or by you for Good Reason (each, as defined below)
     within the twenty-four (24) month period immediately following or the two
     month period immediately prior to a Change of Control (as defined below),
     in addition to the Accrued Obligations, and contingent on your provision of
     a timely release of claims against the Company, you shall be entitled to
     receive:

                      (A)   continuation of your Base Salary in effect at the
     time of termination for the period of twelve (12) months following the
     termination. To the extent required by Section 409A of the Code, the first
     installment of such Base Salary in the amount of six (6) months' Base
     Salary shall be payable on the first business day following the six (6)
     month anniversary of the effective date of termination, and the remainder
     shall be payable in accordance with the Company's regular payroll
     procedures thereafter. If Section 409A of the Code is not then applicable,
     such Base Salary continuation shall commence immediately from the date of
     termination.

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Thomas G. Auchincloss, Jr.
September 18, 2006
Page 4

                      (B)   In addition, should the award of a Bonus have become
     customary, you shall be entitled to a payment equal to the average of the
     Bonuses paid to you (if any) in the two years preceding the termination, to
     be paid (A) on the first business day following the six (6) month
     anniversary of the effective date of termination, to the extent required by
     Section 409A of the Code, or (B) if Section 409A of the Code is not then
     applicable, within thirty (30) days following the termination.

                      (C)   continued payment of COBRA premiums to maintain
     medical and dental benefits, if any, in effect at the time of termination
     for the period of twelve (12) months following the termination; and

                      (D)   full vesting of all options and restricted stock
     granted to you under the Metabolix Inc. 1995 Stock Plan, the Metabolix Inc.
     2005 Stock Plan or any authorized successor stock plan provided that the
     conditions to vesting other than the passage of time have been satisfied.

               (ii)   You agree that the payments and benefits hereunder, and
     under all other contracts, arrangements or programs that apply to you (the
     "Company Payments"), shall be reduced to an amount that is one dollar less
     than the amount that would trigger an excise tax under Section 4999 of the
     Code, as determined in good faith by the Company's independent public
     accountants, PROVIDED, HOWEVER, that the reduction shall occur only if the
     reduced Company Payments received by you (after taking into account further
     reductions for applicable federal, state and local income, social security
     and other taxes) would be greater than the unreduced Company Payments to be
     received by you minus (i) the excise tax payable with respect to such
     Company Payments under Section 4999 of the Code; and (ii) all applicable
     federal, state and local income, social security and other taxes on such
     Company Payments. You and the Company agree to cooperate in good faith with
     each other in connection with any administrative or judicial proceedings
     concerning the existence or amount of golden parachute penalties with
     respect to payments or benefits that you receive.

          (d)  "CAUSE". As used herein, "Cause" shall be defined as (i) your
     conviction for, or plea of nolo contendere, to a felony or a crime
     involving moral turpitude, (ii) your commission of a material act of
     personal dishonesty or a breach of fiduciary duty involving personal profit
     in connection with your employment by the Company, (iii) your commission of
     an act which the Board of Directors shall reasonably have found to have
     involved willful misconduct or gross negligence on your part in the conduct
     of your duties under this Agreement, (iv) your habitual absenteeism, (v)
     your material breach of any material provision of this Agreement continuing
     for thirty days after your receipt of written notice thereof from the
     Company, or (vi) the willful and continued failure by you to perform
     substantially your duties with the Company (other than any such failure
     resulting from your incapacity due to physical or mental illness).

          (e)  "CHANGE OF CONTROL". As used herein, a "Change of Control" shall
     occur or be deemed to have occurred only upon any one or more of the
     following events:

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Thomas G. Auchincloss, Jr.
September 18, 2006
Page 5

               (i)    a merger or consolidation of the Company other than a
          merger or consolidation which would result in the voting securities of
          the Company outstanding immediately prior thereto continuing to
          represent (either by remaining outstanding or by being converted into
          voting securities of the surviving entity or the parent of such
          corporation) at least fifty percent (50%) of the total voting power
          represented by the voting securities of the Company or such surviving
          entity or parent of such corporation outstanding immediately after
          such merger or consolidation;

               (ii)   the sale or disposition by the Company of all or
          substantially all of the Company's assets; or

               (iii)  any one person, entity or group, who is not a shareholder
          at time of execution of this Agreement, acquires ownership of capital
          stock of the Company that, together with the capital stock of the
          Company already held by such person, entity or group, constitutes more
          than 50% of the total fair market value or total voting power of the
          capital stock of the Company; provided, however, if any one person,
          entity or group is considered to own more than 50% of the total fair
          market value or total voting power of the capital stock of the
          Company, the acquisition of additional capital stock by the same
          person, entity or group shall not be deemed to be a Change of Control,
          and further provided that the foregoing shall not be deemed a Change
          of Control if the average stock price paid for each share of stock
          held by the person, entity or group is less than $8.00/share (provided
          that such price shall be adjusted as appropriate to reflect any stock
          dividend, stock split, or recapitalization of the Company after the
          date of this agreement).

          (f)  "Good Reason" shall be defined as, in the absence of a cure by
     the Company within 30 days after written notice by you to the Board, a (i)
     a change in title of Chief Financial Officer and Vice President, Finance
     and Corporate Development, (ii) a material diminution of responsibilities,
     duties or powers, (iii) a reduction in Base Salary, Target Bonus, vacation
     or other benefits, except that benefits need only be substantially
     equivalent, or (iv) a requirement that you relocate your principal place of
     employment to (or that you travel more than 50 days in any calendar year to
     the Company's principal place of business in) a location more than 50 miles
     from its current location in Cambridge, Massachusetts, PROVIDED THAT you
     must provide the Company with at least thirty (30) days advance written
     notice of your intent to terminate your employment hereunder and an
     opportunity to cure.

     5.   NONCOMPETITION, NONDISCLOSURE AND INVENTIONS OBLIGATIONS. Your
Employee Noncompetition, Nondisclosure and Inventions Agreement dated May 12,
2005, shall continue in full force and effect in accordance with its terms.

<Page>

Thomas G. Auchincloss, Jr.
September 18, 2006
Page 6

     6.   DISCLOSURE TO FUTURE EMPLOYERS. You will provide, and the Company, in
its discretion, may similarly provide, a copy of the covenants contained in The
Employee Noncompetition, Nondisclosure and Inventions Agreement to any business
or enterprise which you may, directly or indirectly, own, manage, operate,
finance, join, control or in which you may participate in the ownership,
management, operation, financing, or control, or with which you may be connected
as an officer, director, employee, partner, principal, agent, representative,
consultant or otherwise.

     7.   REPRESENTATIONS. You hereby represent and warrant to the Company that
you understand this Agreement, that you enter into this Agreement voluntarily
and that your employment under this Agreement will not conflict with any legal
duty owed by you to any other party.

     8.   GENERAL.

          (a)  NOTICES. All notices, requests, consents and other communications
     hereunder which are required to be provided, or which the sender elects to
     provide, in writing, will be addressed to the receiving party's address set
     forth above or to such other address as a party may designate by notice
     hereunder, and will be either (i) delivered by hand, (ii) sent by overnight
     courier, or (iii) sent by registered or certified mail, return receipt
     requested, postage prepaid. All notices, requests, consents and other
     communications hereunder will be deemed to have been given either (i) if by
     hand, at the time of the delivery thereof to the receiving party at the
     address of such party set forth above, (ii) if sent by overnight courier,
     on the next business day following the day such notice is delivered to the
     courier service, or (iii) if sent by registered or certified mail, on the
     fifth business day following the day such mailing is made.

          (b)  ENTIRE AGREEMENT. This Agreement, together with any Stock Option
     Agreements executed by you and the Company (either prior to or in
     conjunction with this Agreement), the Employee Noncompetition,
     Nondisclosure and Inventions Agreement and the other agreements
     specifically referred to herein, embodies the entire agreement and
     understanding between the parties hereto with respect to the subject matter
     hereof and supersedes all prior oral or written agreements and
     understandings relating to the subject matter hereof, including without
     limitation the Employment Agreement between you and the Company dated
     January 10, 2006. No statement, representation, warranty, covenant or
     agreement of any kind not expressly set forth in this Agreement will
     affect, or be used to interpret, change or restrict, the express terms and
     provisions of this Agreement.

          (c)  MODIFICATIONS AND AMENDMENTS. The terms and provisions of this
     Agreement may be modified or amended only by written agreement executed by
     the parties hereto.

          (d)  WAIVERS AND CONSENTS. The terms and provisions of this Agreement
     may be waived, or consent for the departure therefrom granted, only by
     written document executed by the party entitled to the benefits of such
     terms or provisions. No such waiver or consent

<Page>

Thomas G. Auchincloss, Jr.
September 18, 2006
Page 7

     will be deemed to be or will constitute a waiver or consent with respect to
     any other terms or provisions of this Agreement, whether or not similar.
     Each such waiver or consent will be effective only in the specific instance
     and for the purpose for which it was given, and will not constitute a
     continuing waiver or consent.

          (e)  ASSIGNMENT. The Company may assign its rights and obligations
     hereunder to any person or entity that succeeds to all or substantially all
     of the Company's business or that aspect of the Company's business in which
     you are principally involved or to any Company Affiliate. You may not
     assign your rights and obligations under this Agreement without the prior
     written consent of the Company and any such attempted assignment by you
     without the prior written consent of the Company will be void.

          (f)  GOVERNING LAW. This Agreement and the rights and obligations of
     the parties hereunder will be construed in accordance with and governed by
     the law of Massachusetts, without giving effect to the conflict of law
     principles thereof.

          (g)  JURISDICTION, VENUE AND SERVICE OF PROCESS. Any legal action or
     proceeding with respect to this Agreement will be brought in the courts of
     Massachusetts or of the United States of America for the District of
     Massachusetts. By execution and delivery of this Agreement, each of the
     parties hereto accepts for itself and in respect of its property, generally
     and unconditionally, the exclusive jurisdiction of the aforesaid courts.

          (h)  SEVERABILITY. The parties intend this Agreement to be enforced as
     written. However, if any portion or provision of this Agreement is to any
     extent declared illegal or unenforceable by a duly authorized court having
     jurisdiction, then the remainder of this Agreement, or the application of
     such portion or provision in circumstances other than those as to which it
     is so declared illegal or unenforceable, will not be affected thereby, and
     each portion and provision of this Agreement will be valid and enforceable
     to the fullest extent permitted by law.

          (i)  HEADINGS AND CAPTIONS. The headings and captions of the various
     subdivisions of this Agreement are for convenience of reference only and
     will in no way modify or affect the meaning or construction of any of the
     terms or provisions hereof.

          (j)  ACKNOWLEDGMENTS. You hereby acknowledge and recognize that the
     enforcement of any of the provisions in this Agreement and the
     Noncompetition, Nondisclosure and Inventions Agreement may potentially
     interfere with your ability to pursue a proper livelihood. You represent
     that you are knowledgeable about the business of the Company and further
     represent that you are capable of pursuing a career in other industries
     other than the field of noncompetition as set forth in the Noncompetition,
     Nondisclosure and Inventions Agreement to earn a proper livelihood. You
     recognize and agree that the enforcement of the Noncompetition,
     Nondisclosure and Inventions Agreement is necessary to ensure the
     preservation, protection and continuity of the business, trade secrets and
     goodwill of the Company. You agree that, due to the proprietary nature of
     the

<Page>

Thomas G. Auchincloss, Jr.
September 18, 2006
Page 8

     Company's business, the restrictions set forth in the Noncompetition,
     Nondisclosure and Inventions Agreement are reasonable as to time and scope.

          (k)  TAXES. All payments required to be made by the Company to you
     under this Agreement shall be subject to the withholding of such amounts
     for taxes and other payroll deductions as the Company may reasonably
     determine it should withhold pursuant to any applicable law or regulation.
     To the extent applicable, it is intended that this Agreement comply with
     the provisions of Section 409A of the Code, and this Agreement shall be
     construed and applied in a manner consistent with this intent. In the event
     that any severance payments or benefits hereunder are determined by the
     Company to be in the nature of nonqualified deferred compensation payments,
     you and the Company hereby agree to take such actions as may be mutually
     agreed to ensure that such payments or benefits comply with the applicable
     provisions of Section 409A of the Code and the official guidance issued
     thereunder. Notwithstanding the foregoing, the Company does not guarantee
     the tax treatment or tax consequences associated with any payment or
     benefit arising under this Agreement.

          (l)  COUNTERPARTS. This Agreement may be executed in two or more
     counterparts, and by different parties hereto on separate counterparts,
     each of which will be deemed an original, but all of which together will
     constitute one and the same instrument.

     If the foregoing accurately sets forth our agreement, please so indicate by
signing and returning to us the enclosed copy of this Agreement.

                                           Very truly yours,

                                           Metabolix, Inc.

                                           By: /s/ James J. Barber
                                              ----------------------------------
                                           Name: James J. Barber
                                           Title: President & CEO

ACCEPTED AND APPROVED:

/s/ Thomas G. Auchincloss, Jr.              9/22/06
-------------------------------            ---------------
Thomas G. Auchincloss, Jr.                 Date

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