ATHLETICS Marion Jones was exonerated from doping allegations yesterday after her B-sample for EPO proved to be negative. It therefore failed to confirm the analysis of the original A sample and means the American sprinter will now not be given a two-year ban and is free to compete again at the multi-million pound International Association of Athletics Federations world final in Stuttgart this weekend.

The failure to produce an EPO confirmation on a major track and field star has happened before - in 2003 the then-Kenyan and current US middle-distance runner Bernard Lagat was cleared when a second urine sample tested negative.

Jones, winner of a record five medals at the 2000 Olympics, including three gold, has been dogged by drug allegations since 2003.

She described herself as "ecstatic" and her lawyers claimed it cast a major doubt over the entire worldwide dope-testing system.

"There certainly seem to be issues with the EPO test," said Howard Jacobs, her lawyer. "Maybe it's just a bad test. Maybe you can run the test perfectly and get disparate results. I think they should just scrap the test. They're funding research for a new test for (human growth hormone) but maybe they should make EPO a higher priority. This (EPO test) has been a long-term problem."

If protocol had been followed, Jones' A-sample would never have been leaked as it was last month. Under United States Anti-Doping Agency (USADA) regulations, positives are supposed to be announced only after the second, or B, sample is tested and comes up positive.

"It's certainly as perfect an illustration as you can have of why it's so wrong to publicise an A sample," Jacobs said.

"I would hope that federations would look at that and correct their abuses. But I don't think they will. USADA loves to claim they're out to protect clean athletes. The rules are there to protect clean athletes, too. When federations violate the rules, they are harming clean athletes like Marion."

Jones may now compete in Germany on Sunday, although a more realistic comeback date is at the World Cup in Athens next week.

"I am absolutely ecstatic," she said in a statement. "I have always maintained that I have never ever taken performance enhancing drugs, and I am pleased that a scientific process has now demonstrated that fact. I am anxious to get back on the track."

Jones allegedly tested positive for EPO on June 23rd, after winning the 100 metres at the US nationals for her first sprint title since 2002. She withdrew from the 200m next day and from the Golden League meeting in Zurich last month after she was informed of the positive test.

The IAAF last night refused to comment as it had not received official notification of the B-sample, although it will not be pleased. The sport, having had so much negative publicity from this positive test and that of the world and Olympic 100m champion Justin Gatlin, is now having to defend its drug-testing policy.

But Dick Pound, chairman of the World Anti-Doping Agency, said: "EPO is open to interpretation. Maybe the first one was made too hastily. You wouldn't think there would be variations between the amounts in sample A and sample B. I'm sure there will be some explanation forthcoming from the lab or from USADA. I think the test is good, you just have to know how to read it."

Senior sources involved in drugs testing last night said one possible explanation was that too much time had elapsed between the sample being taken in June and then tested.

It is already established that samples containing EPO can be corrupted in a relatively short space of time.

• Guardian Service