Drug testing has to keep up with the cheats
And they estimate that 2012 could be the first Olympics to have artificially produced super-athletes in action.
A conference on Friday on genes in sport warns that gene therapy - originally devised to help treat diseases like cystic fibrosis - could be abused to enhance performance.
And some sports scientists believe that work must start now on developing tests to catch out the cheats.
Drugs dangers
The International Olympic Committee is concerned and has already set up an advisory group on gene doping.
Three years ago an entire team was thrown out of the Tour de France after cyclists were found to be taking erythropoetin (EPO).
This hormone increases the number of red blood cells, raising oxygen supply in the body and, in so doing, improving an athlete's endurance.
But it also thickens the blood - and at least 20 cyclists are thought to have died from EPO use as a result.
However, in today's competitive world of sport, many athletes are prepared to risk their health - and reputation - in order to win.
Steroid scandal
Canadian sprinter Ben Johnson created the biggest Olympic drugs scandal in 1988.
He was stripped of his 100-metre title and world record after being tested positive for performance-enhancing steroid.
But sportsmen have been known to have genetic advantages quite naturally.
One Olympic cross-country skier had a medal winning mutation: his blood was naturally loaded with up to 50% more red blood cells which boosted his stamina.