Athletics chiefs gave the green light on Monday for all urine samples from August's World Athletics Championships to be re-tested for the new designer steroid THG.
The International Olympic Committee-accredited laboratory in Paris has been told it can start re-testing 400 samples for the tweaked steroid at the centre of a scandal in the sport, an International Association of Athletics Federations spokesman said.
The recent discovery of THG, or tetrahydrogestrinone, has rocked athletics to its core less than a year before the Athens Olympics.
Britain's European champion sprinter Dwain Chambers was the latest athlete to become embroiled in the affair.
He was suspended with immediate effect on Friday after UK athletics confirmed that a positive out-of-competition test he had given in August was supported by the results of his B test.
Chambers, who denies knowingly taking any banned substance or in any way trying to cheat, will now face an independent Disciplinary Committee where he can put his case.
He faces an automatic two-year ban if found guilty by the hearing. Under the IAAF's rule of strict liability, the fact that Chambers does not know how the substance got into his body will not act as a defence.
DOPING TESTS
The Olympic and professional sports world was shocked last month when the U.S. Anti-Doping Agency reported that a new undetectable steroid -- THG -- had been created that would allow elite athletes to pass doping tests.
Steroids are used to improve performance and help athletes recover faster from training.
THG has been tweaked by chemists to make it undetectable under normal testing methods.
The USADA discovered THG when an unnamed track and field coach provided it with the names of U.S. and international athletes who he said were using the steroid.
The coach gave USADA a used syringe that contained some of the substance.
The IOC-accredited laboratory in Los Angeles identified the substance and developed a test for it.
Within days, details of the test were rolled out to all 30 IOC-accredited laboratories around the world.