HealthCor, a New York investment firm, is stepping up its pressure on Trimeris to sell the company.

In a letter sent to Trimeris (Nasdaq: TRMS) and filed with the Securities and Exchange Commission, HealthCor also said it wanted two seats on the biopharmaceutical firm’s board. HealthCor is the largest shareholder in Trimeris with more than 17 percent of the company’s stock.

Trimeris, which makes the HIV drug Fuzeon, has gone through several management changes, a restructuring, and has ceased research and discover efforts. However, Trimeris does want to pursue continued development of another AIDS drug candidate, according to a new strategic plan announced in December. Trimeris also named Martin Mattingly as its chief executive officer in November.

Last week, Trimeris reported that sales of Fuzeon dropped 9 percent in the fourth quarter of 2007 from the same period a year ago. Sales dipped to $66.5 million in the quarter, down from $73.9 million in the previous three months. A sharp drop of 25 percent in the U.S. and Canadian market to $31.5 million offset a 13 percent increase for international sales to $35 million.

For the year, Fuzeon sales increased 7 percent to $266.8 million from $249 million in 2006.

In its letter, HealthCor said it preferred that Trimeris find a buyer. HealthCor added that it had been unable to reach Trimeris board member Julian Baker.

“On February 1, 2008, HealthCor Management, L.P. sent a letter to the Board of the Issuer reiterating HealthCor Management, L.P.’s concerns with regard to the Issuer’s strategic direction, including the continued development of TRI-1144,” HealthCor said in a second SEC filing.

“HealthCor Management, L.P. stated that the Issuer should pursue a sale transaction, should not pursue acquisitions, and should return its excess cash to the shareholders,” the firm added. “Given the importance of the decisions that face the Issuer and their potential dramatic impact on shareholder value, HealthCor Management, L.P. advised the Issuer that it sought representation on the Board and proposed two members of the firm, Arthur Cohen and Evan Sturza, to serve on the Issuer’s Board.”

Trimeris shares closed at $6.59, up 19 cents, on Monday.

See the Web link with this item for the full contents of the letter.