Spanish cyclist Maria Isobel Moreno became the first athlete to fail a doping test here at the Olympic Games, the IOC revealed on Monday.
The 27-year-old tested positive for EPO having undergone the test on July 31. She left the athletes' village on the evening of the 31st before she knew of the results of the test.
Giselle Davies, IOC spokeswoman, announced Moreno's positive test.
"The IOC means business in stamping out doping," she said. "The test of the athlete revealed that she had tested positive for EPO.
"Moreno left China the evening of the test, before she knew of the results. Her accreditation has been cancelled and withdrawn by the IOC. We have asked the sport's governing body, the International Cycling Union (UCI) to follow it up as any disciplinary measures will be complete after the Games finish."
Moreno had been considered one of Spain's best hopes for a women's cycling medal, in the road race.
Spanish sports officials here described the scandal as "sad" but stressed that they were convinced it was an isolated case.
"If this is confirmed, it represents an act of irresponsibility," said Spain's sports minister Jaime Lissavetsky. "It's a sad situation and the federation should open an inquiry to discover who put this idea into the cyclist's head."
The president of the Spanish Olympic Committee, Alejandro Blanco, said three weeks ago that there would not be a single Spanish drugs failure at the Games and that all of the country's 286 competitors "are clean".
In a statement on Saturday, Moreno apologized to the Spanish public and said she would "explain and defend" her reasons for dropping out of the women's road race and the time trial at a press conference on Monday in the Spanish north-eastern city of Zaragoza.
Moreno had announced on Thursday she would not be taking part in the Games after what has been described in the Spanish media as an "anxiety attack".
The technical director of the Spanish cycling federation, Mikel Zabala, has said that Moreno's decision was "personal".
IOC President Jacques Rogge had said on the eve of the Games that he expected there to be between 30-40 positive tests at the Games.