**EXHIBIT 31.1**

 

**CERTIFICATION**

 

I, Richard P. Eno certify that:

 

1.             I have reviewedthis quarterly report on Form 10-Q of Metabolix, Inc.;

 

2.             Based on myknowledge, this report does not contain any untrue statement of a materialfact  or omit to state a material factnecessary to make the statements made, in light of the circumstances underwhich such statements were made, not misleading with respect to the periodcovered by this report;

 

3.             Based on myknowledge, the financial statements, and other financial information includedin this report, fairly present in all material respects the financialcondition, results of operations and cash flows of the registrant as of, andfor, the periods presented in this report;

 

4.             The registrant’sother certifying officer(s) and I are responsible for establishing andmaintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and15d-15(e)) and internal control over financial reporting (as defined inExchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant andhave:

 

(a)     Designed such disclosurecontrols and procedures, or caused such disclosure controls and procedures tobe designed under our supervision, to ensure that material information relatingto the registrant, including its consolidated subsidiaries, is made known to usby others within those entities, particularly during the period in which thisreport is being prepared;

 

(b)     Designed such internalcontrol over financial reporting, or caused such internal control overfinancial reporting to be designed under our supervision, to provide reasonableassurance regarding the reliability of financial reporting and the preparationof financial statements for external purposes in accordance with generallyaccepted accounting principles;

 

(c)     Evaluated the effectivenessof the registrant’s disclosure controls and procedures and presented in thisreport our conclusions about the effectiveness of the disclosure controls andprocedures, as of the end of the period covered by this report based on suchevaluation; and

 

(d)     Disclosed in this report anychange in the registrant’s internal control over financial reporting thatoccurred during the registrant’s most recent fiscal quarter (the registrant’sfourth fiscal quarter in the case of an annual report) that has materiallyaffected, or is reasonably likely to materially affect, the registrant’sinternal control over financial reporting; and

 

5.             The registrant’sother certifying officer(s) and I have disclosed, based on our most recentevaluation of internal control over financial reporting, to the registrant’sauditors and the audit committee of the registrant’s board of directors (orpersons performing the equivalent functions):

 

(a)     All significant deficienciesand material weaknesses in the design or operation of internal control overfinancial reporting which are reasonably likely to adversely affect theregistrant’s ability to record, process, summarize and report financialinformation; and

 

(b)     Any fraud, whether or notmaterial, that involves management or other employees who have a significantrole in the registrant’s internal control over financial reporting.

 

 
| Date: May 7, 2009 | /s/   RICHARD P.  ENO |
|------------------------|---------------------------------|
|                   | Name:                           | Richard P. Eno |
|                   | Title:                          | *President and Chief Executive  Officer  (Principal Executive Officer)* |

 

----