SAN FRANCISCO - Olympic gold-medal sprinter Antonio Pettigrew admitted Thursday for the first time that he took performance-enhancing substances during a long, successful track career in which he passed all drugs tests.

The admission came during testimony in the trial of his former coach Trevor Graham, who is accused of lying to federal authorities investigating doping in sports. Graham has pleaded not guilty.

Pettigrew, now an assistant track coach for UNC-Chapel Hill, testified that Graham encouraged him in 1997 to inject human growth hormone and the oxygen-boosting drug EPO, which are both banned in track. Soon after, Pettigrew said, he began buying the drugs from Angel “Memo” Heredia, an admitted steroids dealer from Laredo, Texas.

Once he began taking the banned substances, Pettigrew said he was able to run 400 meters faster than 43 seconds for the first time.

“I was running incredible times as I was preparing for track meets,” Pettigrew said during 30 minutes of testimony. “I was able to recover faster.”

Pettigrew initially lied to federal investigators and denied doping when they first talked to him in February 2005. But he finally confessed to cheating when confronted with documents in October 2006 strongly suggesting drug buys from Heredia.

UNC head coach Dennis Craddock said Thursday that Pettigrew was still an assistant but had no comment when asked whether the former sprinter would remain on Carolina's staff.

Pettigrew won a gold medal as part of the 1,600-meter relay team at the 2000 Sydney Olympics. He retired from track in 2002.

When faced in 2003 with the prospect of losing his medal after teammate Jerome Young's positive test was revealed, Pettigrew reacted strongly.

"If anything comes down to where I'm supposed to be giving my medal back, I'm taking some action against some organization," he said at the time.

In July 2004, the International Association of Athletics Federations, the world governing body for track, recommended to the International Olympic Committee that the entire relay team be stripped of its gold medals. But the Court of Arbitration for Sport upheld an appeal by the U.S. Olympic Committee and athletes Pettigrew, Michael Johnson, Angelo Taylor, Alvin Harrison and Calvin Harrison. As a result, only Young lost his medal.

The IOC could not be reached for comment, and the USOC has not responded yet to the question of whether Pettigrew and his teammates now stand to lose their medals.

Also Thursday, IRS agent Erwin Rogers testified that Justin Gatlin, the defending Olympic 100-meter champion and another former Graham athlete, worked undercover for the government and secretly recorded several telephone calls with Graham. U.S. District Court Judge Susan Illston barred Rogers from disclosing any more details of the calls.

Gatlin, who has served half of a four-year ban for doping, tested positive for excessive testosterone at the Kansas Relays in 2006, his second doping violation. He has maintained he never knowingly took a performance-enhancing drug.

Gatlin has asked the Court of Arbitration for Sport to cut his suspension nearly in half so he can compete at the Beijing Olympics.