LONDON -- Athletes who tested positive for the steroid THG could get reduced bans from the sport's governing body if they provide information on anybody involved in a doping conspiracy.

Five athletes are under investigation for use of THG, or tetrahydrogestrinone, and face minimum two-year suspensions if found guilty.

The International Association of Athletics Federations has a rule allowing reduced sanctions for athletes offering "substantial assistance in a doping inquiry.

"However, it is emphasized that only truly exceptional circumstances will justify any reduction," the rule states.

IAAF spokesman Nick Davies suggested Monday that British sprinter Dwain Chambers could get a ban cut to one year in exchange for information on those supplying and using THG.

IAAF general secretary Istvan Gyulai said 18 athletes in the past four years have applied for reinstatement or shortened bans on grounds of "exceptional circumstances," with all but two cases rejected by the IAAF.

"We are not like a public prosecutor offering a plea bargain," Gyulai said. "We don't do bargains. We just want a clean sport."

THG was uncovered last summer after an anonymous tip. Four U.S. athletes tested positive for THG at the national championships in June at Stanford, Calif. Chambers, the European 100-meter champion, tested positive in an out-of-competition control in Germany in August.

The IAAF confirmed Monday that retesting of samples from the world championships in Paris in August had begun. The 400 samples are being analyzed for THG in France. Any positive findings would result in retroactive disqualifications, including stripping of any medals, and two-year bans.

Davies said the retesting could take up to three weeks. He said the IAAF expects "no more than a handful" of positive THG tests.

Chambers was suspended last Friday after analysis of his backup B sample confirmed his positive A test. The B test results of the American athletes, including 1,500-meter runner Regina Jabobs and shot putter Kevin Toth, haven't been announced.

Chambers' lawyer insisted Friday the sprinter has never taken performance-enhancing drugs and would fight to clear his name.