A Massachusetts State Senator donated part of his liver to his brother-in-law in a living-related transplant operation at the Lahey Clinic in Burlington.

State Sen. Stephen F. Lynch, 45, donated more than half his liver to his liver to Joseph P. O'Leary, 54, both of South Boston. O'Leary, who is married to Lynch's sister, had been diagnosed with liver cancer.

Dr. Elizabeth A. Pomfret, director of Lahey's adult living-donor transplant program, said Lynch was "beginning the recovery process much quicker than we anticipated" and should resume his full duties within two weeks.

Lahey has the country's third largest living-donor liver transplant program, and the Lynch-O'Leary transplant was the 33d done by the team since 1998, when they performed the first such procedure in New England. At the time, they were at Beth Israel Hospital in Boston, but the entire team moved to Lahey in June 1999.

The Lahey success rate for recipients over living-donor livers is 91.4 percent after two years, and no donor has ever died at Lahey, a hospital spokesman said.