Rumors of drug use have swirled around the Olympic Games since the ancient Greeks, when athletes munched psychedelic mushrooms to boost their performance.
Many other chemical substances thought to give athletes an edge have been tried over the years, and every time officials thought they had a good test to detect illegal drugs, the athletes got trickier and tried something new.
Brandy was followed by caffeine, amphetamines and steroids.
The latest attempt to squeeze a little extra out of the athletes' bodies involves EPO and human growth hormone, which are extremely difficult to detect. EPO stimulates bone marrow to grow red blood cells, which carry extra oxygen and help increase stamina by as much as 15 percent. It is particularly effective in endurance events such as long-distance running, cycling and swimming.
The drug was banned from athletic competitions because it can have dangerous side effects. The blood can get too thick and not flow freely. From 1987 to 1991 circumstantial evidence implicated EPO in the deaths of 18 cyclists in Europe. But athletes continued to use it because it is difficult to detect.
The International Olympic Committee hopes to stop or at least slow down use of the drug at the Sydney Olympics. Last month the IOC approved the first tests for erythropoietin, or EPO, to be administered during this year's Olympics. At least 400 tests are expected to be given between Sept. 2, when the athletes' village opened in Sydney, and Oct. 1 when the Games end.
Athletes will take two EPO tests -- blood and urine -- and be considered guilty only if both tests show positive. It will be the first use of blood tests as part of the official Olympic anti-doping program.
They will be part of some 3,800 drug tests to be conducted before and during the Games, nearly twice as many as were given for the Atlanta Olympics. This is in addition to about 2,000 unannounced tests expected to be given by the World Anti-Doping Agency before the Games even begin.
Ultimately, more than half the athletes competing in Sydney could be tested.
WADA was established in 1999 as an independent agency to work with the groups that govern individual sports and national Olympic committees. The testers show up at the athlete's home or at a competition and demand a sample. The athlete must disrobe from the waist down and provide the sample while the tester watches.
Many athletes dislike the WADA procedure -- called "knock and pee" -- but view it as a necessary step to catch or discourage cheaters.
Scientists hoped to develop a reliable test for human growth hormone, which helps athletes bulk up, but it looks like such a test will not be available for the Sydney Games.
But when such a test is developed someone else will develop another drug even more difficult to detect. Some scientists think the next generation of performance enhancers will be delivered by a virus or bacteria carrying a gene modifier.