Yordanova finished fifth in the 1,500m at the Athens
Bulgarian athlete Daniela Yordanova has been barred from the Olympics after failing a doping test.
Yordanova tested positive for testosterone in an out-of-competition doping test in Sofia on 13 June.
A potential 1,500m medal contender, the 32-year-old Yordanova had been due to fly to Beijing on Saturday.
"She's been tested constantly and all her samples so far were negative," said federation president Dobromir Karamarinov after the positive result.
Yordanova finished fifth in the 1,500m at the Athens Olympics in 2004.
In the past two years, Bulgarian middle-distance runners Vanya Stambolova and Teodora Kolarova, high jumper Venelina Veneva and hammer thrower Andrian Andreev have tested positive.
Spanish cyclist Maria Isabel Moreno became the first athlete to fail a drugs test at the Beijing Olympics earlier this week.
Before Friday, only three athletes had tested positive out of about 2,200 tests after six days of competition.
In Athens there were a total of 26 cases of positive tests or other anti-doping rule violations such as refusal to provide a sample or missed drugs controls from some 3,300 tests.