Fewer Olympics Dopers Raises Suspicion

Performance Enhancing Drugs and Steroids

The increased testing at the Olympics and stepped up pre-Games screening conducted at the national level have ensured cleaner competitions, he said.

"I can't comment exactly on what's going on at the Olympics until after," Howman said. "But, in general, I think we can say there has been a considerable enhancement in the fight due to WADA."

International Olympic Committee spokeswoman Emmanuelle Moro told ABCNews.com that 39 athletes who might have been caught doping in Beijing were caught prior to the Games because of improved pre-policing measures. In 2004, similar pre-Games testing prevented seven athletes from competing in Athens.

Still, anti-doping researchers remained unconvinced that Olympics testing efforts are keeping up with the cheats.

Tim Noakes, a professor of exercise and sports science at the University of Cape Town, South Africa, says that as long as undetectable drugs are available, the assumption is that they are being used.

"If there are fewer than expected positive doping tests, it really does not tell us that fewer athletes are doping," he wrote via e-mail. "It just says that fewer are using drugs that can be detected.

Cheating Olympic Athletes

"Observing the physiques of some successful athletes who have not tested positive suggests that they are using something that is not being detected."

Scientists are working around the clock at a drug-testing lab in Beijing to test for the methods and substances, such as stimulants, steroids, hormones and narcotics, banned by the World Anti-Doping Agency.

But, UCLA's Butch emphasized, athletes are increasingly seeking out short-acting drugs that clear the body very quickly. By monitoring the impact of those drugs on other molecules in the body, scientists have been able to catch cheaters.

Scientists determined last week, for example, that Spanish cyclist Maria Isabel Moreno had used the banned hormone erythropoietin. But because the drug exits the body rapidly it's often difficult for scientists to detect.

Other drugs that are eliminated quickly, Butch said, are composed of insulins and growth hormones. Gene doping is another method that might soon catch on.