His interview is part of preparation for a Feb. 13 public hearing expected to focus on Roger Clemens' denials of allegations about his use of performance enhancers made in the Mitchell report by former personal trainer Brian McNamee.
Clemens's lawyer told The New York Times that they expected Pettitte's statements would help, not hurt, his former teammate.
Pettitte lent credence to former Senate majority leader George Mitchell's findings by acknowledging he received two injections of human growth hormone from McNamee.
A former Yankees teammate of Pettitte and Clemens, Chuck Knoblauch, spoke to committee staff Friday. The day before, an employee of the sports agency that represents Clemens and Pettitte went to Capitol Hill to be interviewed.
McNamee said he injected Clemens with HGH and steroids in 1998, 2000 and 2001. The seven-time Cy Young Award winner has denied the allegations repeatedly and in various settings -- but not under oath.
McNamee also told Mitchell he injected Pettitte two to four times with HGH -- and two days after the report was released in December, Pettitte said he took HGH for two days to deal with an elbow injury in 2002.
The 35-year-old Pettitte, who won four World Series championships with the Yankees, returned to the team last season and went 15-9. This offseason, he put off retirement and agreed to a $16 million, one-year contract to play for the Yankees next season.