Exhibit 31.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER

I, Ming Hsieh, President and Chief Executive Officer of
Cogent, Inc. (the Registrant), certify that:

1. I have reviewed this quarterly report on Form 10-Q of the Registrant;

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

3. Based on my knowledge, the financial statements, and other financial information included in this quarterly report, fairly present in all material
respects the financial condition, results of operations and cash flows of the Registrant as of, and for, the periods presented in this quarterly report;

4. The Registrants other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal
control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the Registrant and we have:

(a) designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated
subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b) designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of
financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c) evaluated the effectiveness of the registrants disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end
of the period covered by this report based on such evaluation; and

(d) disclosed in this report any change in the
registrants internal control over financial reporting that occurred during the registrants most recent fiscal quarter (the registrants fourth fiscal quarter in the case of an annual report) that has materially affected, or is
reasonably likely to materially affect, the registrants internal control over financial reporting; and

5. The Registrants
other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the Registrants auditors and the audit committee of Registrants board of directors:

(a) all significant deficiencies and material weaknesses in the design or operation of internal controls over financial reporting which
are reasonably likely to adversely affect the Registrants ability to record, process, summarize and report financial information; and

(b) any fraud, whether or not material, that involves management or other employees who have a significant role in the Registrants internal controls over financial reporting.

Dated: August 8, 2006



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|/s/    MING HSIEH                    
|Ming Hsieh                           
|President and Chief Executive Officer
|(Principal Executive Officer)