**EXHIBIT 31.1**

 

**CERTIFICATION**

 

I, Richard P. Eno, President,Chief Executive Officer and Principal Executive Officer of Metabolix, Inc.,certify that:

 

1.             I have reviewed thisquarterly report on Form 10-Q of Metabolix, Inc.;

 

2.             Based on my knowledge, this reportdoes not contain any untrue statement of a material fact  or omit to state a material fact necessary tomake the statements made, in light of the circumstances under which suchstatements were made, not misleading with respect to the period covered by thisreport;

 

3.             Based on my knowledge, thefinancial statements, and other financial information included in this report,fairly present in all material respects the financial condition, results ofoperations and cash flows of the registrant as of, and for, the periodspresented in this report;

 

4.             The registrant’s othercertifying 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 suchdisclosure controls and procedures, or caused such disclosure controls andprocedures to be designed under our supervision, to ensure that materialinformation relating to the registrant, including its consolidatedsubsidiaries, is made known to us by others within those entities, particularlyduring the period in which this report 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 theeffectiveness of the registrant’s disclosure controls and procedures andpresented in this report our conclusions about the effectiveness of the disclosurecontrols and procedures, as of the end of the period covered by this reportbased on such evaluation; and

 

(d)     Disclosed inthis report any change in the registrant’s internal control over financialreporting that occurred during the registrant’s most recent fiscal quarter (theregistrant’s fourth fiscal quarter in the case of an annual report) that hasmaterially affected, or is reasonably likely to materially affect, theregistrant’s internal control over financial reporting; and

 

5.            The registrant’s othercertifying 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 not material, that involves management or other employees who have asignificant role in the registrant’s internal control over financial reporting.

 

 
| Date: May 8, 2008 | /s/   RICHARD P.  ENO |
|------------------------|---------------------------------|
|                   | Name:                           | Richard P. Eno |
|                   | Title:                          | *President and Chief Executive  Officer* |
| * *               | * *                        | *(Principal Executive Officer)* |

 

----