One of the world's leading experts on drugs in sport believes athletes will be able to cheat without detection at next year's Beijing Olympics.
Suspicion will hover over the Games until a robust HGH test is found
Peter Sönksen claims the test for human growth hormone (HGH) is useless and will only catch "a stupid athlete".
"The test we have is imperfect and it's probable that an awful lot of people who appear to be negative are in fact doping," the professor told BBC Sport.
"Until we have a more effective test, you can't believe what you're seeing."
Sönksen, an emeritus professor of endocrinology at St Thomas' Hospital in London and a visiting professor at Southampton University, has studied HGH for over 40 years and during that time has advised the International Olympic Committee (IOC) and the UK authorities on the issue of doping.
His call for urgent action comes with the Beijing Olympics now less than 10 months away and on the day the World Anti-Doping Agency (Wada) starts its Third World Conference on Doping in Sport.
That three-day summit in Madrid has brought together all of the world's leading players in the fight against doping but Sönksen's words will underline just how much still needs to be done.
"We don't know how many (athletes are using HGH), because there isn't a reliable test out there to tell us," the 71-year-old Englishman said.
"All we've got is hearsay. The hearsay is that it's very prevalent. The estimates are that most athletes think that at least half their colleagues are doping.
"Part of the doping procedure is that the coaches know exactly how long a drug is in the system and they work out how to get their athlete to the Games and test negative.
"With growth hormone, as there isn't an effective test, they don't have to bother. They just have to make sure they don't get caught with the drug in their bag."
A recent web-based survey of elite German sportsmen and women - using a new, more accurate method called randomised response technique - threw up some alarming statistics.
The anonymous survey found that at least 25%, and perhaps as many as 48%, of those questioned had used illicit performance-enhancing drugs. The numbers for track and field athletes were even more disturbing, 38% and 63%.
Wada's director general David Howman is under no illusions as to the size of the problem and the particular threat that HGH poses for the integrity of sport (not to mention the health implications of widespread misuse amongst elite athletes).
"Not only is (HGH) used probably with total impunity, it's probably being used in conjunction with other bad substances," Howman told BBC Sport in Madrid.
"So it is of concern to us, it is of importance.
"At the moment, there's a time span during which you can be detected if you've taken it. Outside that time zone, it's undetectable.
"So we've got to get better and the scientists have to continue to work."
When BBC Sport asked IOC boss Jacques Rogge for his response to this story he admitted that the HGH issue was a grave concern for the Olympic movement but remained optimistic that an answer was on the horizon.
"I am being told that they are making progress (in developing a reliable test)," said Rogge.
HUMAN GROWTH HORMONE
Why cheats take it: It stimulates growth in most body tissue, including skeletal muscle (which adds power) and cartilage and tendons (which reduces injuries). It also burns fat and enables athletes to work harder, longer and more often
The side effects: It also promotes bone and internal organ growth. Acromegaly is a thickening of bones, especially in the feet, hands and jaw, while enlarged vital organs, such as the heart, can cause failure. Skin texture changes and it has been linked to diabetes
"So my message to the athletes is be very careful because there might be a test in place for Beijing and I hope that will be the case."
Later on Thursday, UK Sport, the body that runs this country's anti-doping programme, confirmed it is part of a research project, with Southampton University and King's College in London, which is close to finalising an improved HGH test.
"We have been working with this group, led by Professor Sönksen, for about a year and we are confident the solution being developed can fill the gap," said John Scott, UK Sport's director of drug-free sport.
"Such a gap in our testing armoury obviously concerns us as it damages our ability to tackle doping in sport.
"We are actively engaged with Wada on this matter and will be seeking its approval of the (new) test in the near future."
Until then, Sönksen is convinced HGH will remain elite sport's "drug of choice".
Growth hormone occurs naturally in the human body. It is produced by the pituitary gland in the brain and stimulates the growth of muscle, cartilage, and bone.
It is made throughout a person's lifetime but is more plentiful during youth. It stimulates growth in children and plays an important role in adult metabolism.
Its appeal to athletes is that it offers huge potential gains in strength, burns off fat and can even improve stamina, largely because recovery time from rigorous training is reduced.
It is also widely available - as part of this investigation BBC Sport bought 11 vials of a substance described as Chinese HGH from a seller in Indonesia.
The problem with the current test for HGH is that it is only as effective for a very short time after an athlete has taken a dose.
"Growth hormone is cleared so quickly from the blood stream that after 24 hours it's all gone," explained Sönksen.
"So if somebody's injected recombitant (artificially-made) growth hormone, the current blood test hasn't got a chance of picking it up 24 hours later. And in many cases it's even quicker than that."
The frustration for Sönksen is that he has developed a blood test for HGH that is "100 times better" than the one being used now. In fact, it has been available for eight years.
Sönksen led a team of scientists appointed by the IOC to get an HGH test ready for the Sydney Olympics, the project was called GH-2000 and reported its results in January 1999.
This approach is based on the measurement of GH-dependent proteins, or "markers", and has proved to be considerably more effective in detecting HGH doping.
"You can catch a reasonable number of people - 25% anyway - as long as two weeks after the last injection," said Sönksen.
Actor Sylvester Stallone was caught bringing HGH into Australia
But despite the study's science being verified by peer review, the GH-2000 approach was not taken up by the IOC (who then passed the anti-doping responsibility to Wada).
"It isn't used because it hasn't been established in what were the IOC laboratories and now the Wada laboratories. It's a technical issue on getting the test set up and validated," said Sönksen.
"It's expensive to get it set up, but once the test is up and running, it's cheap to run, much cheaper than the mass spectrometry methods (the most common technique used to detect doping)."
Further funding for GH-2000, which had been promised by the IOC, failed to materialise and Sönksen has spent the last eight years "dotting the i's and crossing the t's" of the report.
Wada's Howman admitted that Sönksen's work was important and remained one of the possible solutions to the problem.
"(Sönksen) has been part of the group of scientists who we bring together from time to time to make sure the test that is used is capable of being used at each of our accredited laboratories," said Howman.
"I'm speaking with UK Sport and (King's College London expert) David Cowan to see what we can do to enhance the test that he says is now ready to be put out in the laboratories.
"If we can do that, we'd be stupid not to.
"But we have to aim for close to perfection, we have to achieve it. Sometimes that means a little longer than you would prefer but it must be so."