By Jonathan Overend
BBC Sport tennis commentator
Seven male tennis players have tested positive for the banned steroid nandrolone.
Bohdan Ulihrach was one of the players who tested positive
But, in an extraordinary twist, the ATP, which runs the men's tour, says the players are not to blame - they are themselves.
The ATP has effectively accepted responsibility by saying its own trainers have been handing out black-listed supplements.
The trainers, who travel on the tour helping players with their medical needs, have been giving players electrolyte replacement health products despite warnings not to.
These products are believed to have been used for 20 years without previous incident.
It is a huge embarrassment for the ATP and world tennis.
The International Tennis Federation is believed to be privately furious at how this has arisen.
The ATP says distribution of the supplements has been halted and appropriate action against personnel has been taken.
Between August last year and the middle of May, seven players, including Bohdan Ulihrach, who was given a two-year ban for a doping offence on 2 May, gave samples which showed traces of nandrolone above the legal limit.
Samples from another 36 players showed traces of nandrolone but insufficient to test positive.
Subsequent tests showed a unique similarity between them all, suggesting a single source.
Ulihrach, a former top-30 player from the Czech Republic, has now been cleared after an appeal tribunal heard about the new evidence.
His fine, two year ban and ranking point deduction, have all been dismissed.
"I am very glad and satisfied that the tribunal has confirmed what I stated from the outset; that I am innocent of these charges," he told the ATP website.
"I also want to thank the tribunal for agreeing to my request for a second hearing and making the right decision to let me return to the game."
Interviews with ATP trainers confirmed that he had received a total of nine tablets in the three days before his positive test.
This is why the other six players are unlikely to ever be named.
Questions are bound to be raised about the ATP's handling of the affair.
They, along with the ITF and WTA, are signed up to the World Anti-Doping Code which states that cases on appeal must be handled by the Court of Arbitration for Sport.