Anti-doping laboratories are working on a test to detect a powder used to destroy traces of the performance-enhancer EPO in urine samples.
Martial Saugy, the head of the Swiss anti-doping laboratory, said there have been suspicious tests over the last year in which no traces of EPO -- or Erythropoietin -- were found in athlete's urine, not even natural EPO produced by the body's kidney cells.
Researches suspect cheats are using a substance called protease -- sometimes used in stain removers -- to wipe out all traces of EPO in their urine.
"There has been a significant increase in the number of samples in which there is no EPO detected at all, leading us to believe they are being manipulated," Saugy said on Sunday.
"We have no proof so far but there are indications that a powder exists. It can happen that people who excrete less EPO than others have a result where there is no EPO, but it is unusual. And over this last year we've seen some suspicious cases of EPO-free urine samples, where we did not understand why suddenly it was undetectable," Saugy added.
The research coincides with reports that German cycling pro Jan Ullrich, who was barred from the Tour de France for his alleged involvement in the Spanish doping scandal, had several EPO-devoid samples.
A program aired on Sunday on the Swiss television channel SF1 reported that the head of the anti-doping unit of the Swiss Department for Sport, Matthias Kamber, was instrumental in uncovering the possible scam, noticing that more than a dozen doping samples without EPO had been submitted in Switzerland.
According to the SF1 program, one of the EPO-free doping tests belonged to Ullrich, using a sample reportedly taken in December last year during a training camp in South Africa.
The Swiss newspaper NZZ am Sonntag reported that the Switzerland-based cyclist had at least two further such samples.
NZZ said the possibility that Ullrich could have used protease is supported by documents from the Spanish doping scandal. Documents pertaining to Ullrich mention the word polvos (powder) a number of times, the newspaper said.
Saugy was unable to confirm the allegations.
Scientists are now seeking a test to detect the presence of protease in urine, which is proving tricky.
"These products deteriorate very quickly. ... In urine it [protease] is a product which will be invisible after a certain time. It's not complicated but we still need to work on it," he said.
Protease is cheap, readily available, and the cheating process is simple. Cheaters could slip the powder into a urine sample by putting a hand in their pocket where some protease is stashed, then urinating on their fingers.