Athletes have used a wide range of drugs to boost performance
Scientists have found a way to identify a type of new drug which could be misused by athletes.
The test, developed in Germany, can spot benzothiazepines, a potential heart drug of the future which may boost muscle endurance.
Researchers warned that athletes might be starting to use it even before human trials were completed.
However, a UK expert said the sheer number of new drugs made doping-free sport unlikely.
Although only a handful of athletes at the Beijing Olympics themselves tested positive for banned substances, many anti-doping specialists are suspicious that as-yet unidentified performance-enhancing drugs may have been in use.
Although there is no evidence that benzothiazepines have been used, experts believe it possible that some cheats have already cottoned on to their effects.
The new test, detailed in the journal Drug Testing and Analysis, can pick out their chemical signature, even in tiny concentrations in urine.
The drugs work by making muscle cells more efficient and less likely to suffer fatigue by keeping more calcium in them.
Human trials have yet to start, although animal trials have clearly shown their potential, and the drug can be made easily.
Mario Thevis, from the Center for Preventive Doping Research at the German Sport University of Cologne, said that speed was of the essence.
"As soon as these drugs enter human trials, there is a huge potential for them to be misused in sports.
"This preventive research lets us prepare before these compounds are officially launched."
Professor Barrie Houlihan, from Loughborough University, who chairs the UK Sport Anti-Doping Research Steering Group, welcomed the finding, and stressed the need to keep one step ahead of drug cheats.
One method currently being used to discourage cheats is to keep urine samples for several years so they can be retrospectively checked when new tests are developed.
Samples taken during the Olympics were currently being checked for a newly-discovered blood doping agent, he said.
"We are always wary that there are drugs being used that have not been identified.
"I was told that there are currently 11 different blood boosting drugs around, and we are only able to test for one of them.
"I can't see that we will ever have completely drug-free sport, and we need to be realistic about that, but we have to try to keep pace with the changes in drug use, so that clean athletes have a chance of doing well."