RALEIGH, N.C. -- Calvin Harrison has tested positive for the banned stimulant modafinil, the U.S. Olympic 4x400-meter relay gold medalist told Reuters on Saturday.

"Yes, I tested positive for modafinil at the [U.S.] nationals," Harrison said in a telephone interview from his home in Raleigh.

"I was notified that they [the U.S. Anti-Doping Agency] had tested my A sample and that they would test my B sample, which they probably have by now."

Harrison's modafinil positive is the latest in a series of positive tests that have rocked track and field on both sides of the Atlantic and could leave next year's Olympics in Athens missing a host of banned big-name athletes.

It also followed the discovery of previously undetectable designer steroid tetrahydrogestrinone.

Four U.S. athletes have tested positive for the steroid, American officials have said, as has Britain's European 100 meters champion Dwain Chambers, who said through his lawyer that if he did take the drug, it was unwittingly.

"I did have modafinil in my system," Harrison said. "However, I am not in the least advocating the taking of any illegal substances because I strongly believe in fair play."

Harrison said he was given the substance by a coach in California. But the athlete stressed he had never been given an illegal substance by his current coach, Trevor Graham.

"He [the coach in California] had given me this pill, and I had taken it. He told me it was not a steroid and that it would just keep you 'up' so you wouldn't be so fatigued," said Harrison.

"He emphasized that it was not on the banned substance list and assured me that it was not an illegal substance."

Modafinil is the same stimulant that double world sprint champion Kelli White of the U.S. tested positive for at the world championships in Paris in August.

Though not specified by name on the banned list, modafinil is covered under the stimulants category of "related substances", the International Association of Athletics Federations has said.

White has said she was prescribed the drug for a sleeping disorder. Her case is now under review by the U.S. Anti-Doping Agency, and if she is found to have committed a doping offense, she could lose her Paris gold medals.

Harrison's positive, if confirmed by the testing of his B urine sample, also could put in jeopardy the United States' 4x400 gold medal at the world championships because he ran the opening leg on the Americans' winning team.

He also was a member of the United States' winning 2000 Olympics 4x400 relay team, which could have its gold medal taken away because Jerome Young ran in the early rounds of the relay after failing a 1999 doping test.

The International Olympic Committee has called for an investigation into why Young was allowed to run.

World indoor 1,500 meters record holder Regina Jacobs also has tested positive for THG, The Washington Post and The New York Times have reported, and American and British newspapers also have said U.S. hammer thrower John McEwen has tested positive for a banned substance.

Neither athlete could be contacted by Reuters for comment.