An unnamed rider in the Tour de France has tested positive for the banned substance EPO.
The racer's name has not been released because he has asked for his B sample to be tested, but organisers said it was not one of the leaders.
"This positive test for EPO was carried out in mid-Tour and up to now he is the only rider to test positive on the Tour," said deputy Tour director Daniel Baal.
"We now must wait for the follow-up test that the rider asked for, but I can tell you that it is not one of the race leaders."
The team boss who employs the rider was told about the test on Thursday but decided not to withdraw him.
The last rider to test positive for EPO at the Tour was Spaniard Txema del Olmo, of the Euskaltel team, in 2001.
He withdrew from the race and was subsequently banned from competing in France for three years.