Justin Gatlin, the world and Olympic 100 meter champion and co-world record holder in the event, acknowledged today that he failed a test drug test after a competition in April.

"I have been informed by the United States Anti-doping Agency that after a relay race I ran in Kansas City on April 22, I tested positive for 'testosterone or its precursors'," Gatlin said in a statement reported by the Reuters News Service. "I cannot account for these results, because I have never knowingly used any banned substance or authorized anyone else to administer such a substance to me."

On April 22, Gatlin anchored his Sprint Capitol training group to victory in the 4x100 meter relay at the Kansas Relays in Lawrence, Kansas, not Kansas City as reported.

In May, Gatlin clocked 9.77 seconds in Doha, Qatar, equalling the world record set last year by Jamaican Asafa Powell. Since then, a Gatlin- Powell match has been the most eagerly-anticipated in the sport. Sidelined with injury, Gatlin hasn't raced since winning the 100 meter title at the U.S. championships on June 23. In his statement, he did not reveal when he became aware of the positive test.

Gatlin said that he has been "doing everything in my power" to determine what caused the positive finding and that he has fully cooperated with the investigation.

"I have been and will continue to cooperate fully with USADA as it moves forward with the process it has initiated and hope that when all the facts are revealed it will be determined that I have done nothing wrong."

One of the most high profile athletes in track and field, Gatlin could face the prospect of a lifetime ban if he's unable to prove his innocence. In 2001, Gatlin was given a two-year ban for amphetamine, which was contained in subscription medication he had been taking for ten years to treat attention deficit disorder. He was later permitted to resume competition a year later and in 2003 won the world indoor title in the 60 meters. Since winning the 2004 Olympic title, Gatlin has been among the most active athletes speaking out against the use of drugs in sports.

"USA Track & Field is gravely concerned that Justin Gatlin has tested positive for banned substances," said USA Track & Field CEO Craig Masback in a statement. "Justin has been one of the most visible spokespersons for winning with integrity in the sport of track and field, and throughout his career he has made clear his willingness to take responsibility for his actions."

"Although difficult," Masback's statement continued, "his case demonstrates that in track and field and Olympic sports, it doesn't matter who you are. If you test positive for a banned substance, you will face substantial consequences. We hope Justin has not committed a doping offense, and we await the completion of the adjudication process."