Revolving Credit Loan Agreement

Exhibit 10.2

As of March 14, 2006

Harvard Bioscience, Inc.

84 October Hill Road

Holliston, MA 01746

Ladies and Gentlemen:

Reference is made to a revolving line of credit in the amount not to exceed $20,000,000 in the aggregate (the “Line of Credit”) made available by Brown Brothers Harriman & Co. (“BBH”) as agent on behalf itself and Bank of America, N.A., f/k/a Fleet National Bank (“BA”) to Harvard Bioscience, Inc. (the “Borrower”) pursuant to a Revolving Credit Loan Agreement by and among BBH, BA, and the Borrower and dated as of November 21, 2003 (the “Credit Agreement”). Obligations of the Borrower arising under the Line of Credit are evidenced by two (2) Revolving Credit Notes, each in the principal amount of $10,000,000 dated as of November 21, 2003, one of which is executed by the Borrower in favor of BBH (the “BBH Revolving Note”), and the second of which is executed by the Borrower in favor of BA (the “BA Revolving Note”). Capitalized terms not otherwise defined herein shall have the meaning ascribed to such terms in the Credit Agreement.

The Borrower’s obligations under the Credit Agreement, the BBH Revolving Note and the BA Revolving Note (the “Obligations”) are secured by, among other collateral, Pledged Collateral as defined and described in a Pledge Agreement dated as of November 21, 2003 by and between BBH as agent, and the Borrower (the “Pledge Agreement”). The Borrower’s Obligations are guaranteed, pursuant to a US Subsidiary Guaranty dated as of November 21, 2003 (the “Guaranty”) by and among BBH as agent, HBIO Securities Corp., Hoefer, Inc., Warner Instruments, Inc., Union Biomerica, Inc., Genomic Solutions, Inc., Cartesian Technologies, Inc., Genomic Solutions Canada, Inc., and Harvard Apparatus, FSC, Inc. (collectively, the “Guarantors”).

The Borrower has requested, and BBH and BA have agreed, to extend the Maturity Date (as defined in the Credit Agreement), provided that the Borrower agrees to certain modifications to the Credit Agreement, the BBH Revolving Note, and the BA Revolving Note. Now therefore, for good and valuable consideration, the receipt and sufficiency of which is hereby acknowledged, and BBH, the Borrower, and BA agree to modify the Credit Agreement, the BBH Revolving Note and the BA Revolving Note as follows:

Paragraph 1.1 of the Credit Agreement is hereby deleted in its entirety, and the following is substituted therefore:

“1.1 Recitals; Maximum Line Commitment . The Borrower wishes to establish a revolving line of credit (the “ Line of Credit ”) with the Lenders in an aggregate principal amount at any one time outstanding not to exceed Twenty Million Dollars ($20,000,000) (the “ Maximum Line Commitment ”), to expire January 1, 2007 (the “ Maturity Date ”).”

Each of the BBH Revolving Note and the BA Revolving Note is hereby amended by deleting “November 21, 2006” from the thi