Competitors were tested for human growth hormone (HGH) for the first time during the Olympics in Athens, World Anti-Doping Agency chief Dick Pound has confirmed.
Pound estimated that 300 samples - about 10 per cent of all drugs tests in Athens - were conducted for the hormone. A record 24 athletes produced positive tests but none of them were for hormone growth hormone.
However, the samples have been preserved and could be retested "if there is a possibility that future knowledge will help us have a better test" the New York Times reports.
The samples are being frozen in the Athens laboratory used during the Games, and can be tested for the hormone, blood manipulation and new designer drugs.
Under WADA rules, samples can be tested and athletes punished for up to eight years after the Games. Pound said: "We are going to try and surprise people with the tests of the so-called designer drugs out there. And we think there may be some people, as was the case in Salt Lake City, that took something that was undetectable, but now is."
The International Olympic Committee retested samples from the 2002 Salt Lake City Winter Olympics for tetrahydrogestrinone, the designer steroid at the heart of the BALCO investigation.
Olympic and drug officials were deliberately vague about the test for HGH before and during the Games. It is considered one of the most widely used banned substances in sport and works like an anabolic steroid, helping to increase muscle mass and quickens an athlete's recovery.
Previously it had not been possible to distinguish between the naturally produced hormone and the synthetic version.