Two Olympic medalists are among six athletes who failed a drugs test after the re-testing of 2008 Beijing Olympic Games samples.
The International Olympic Committee (IOC) said on Thursday that re-testing for the hormone Cera had led to seven positive tests.
Bahrain athlete Rashid Ramzi, who won gold in the 1500m and Italian cyclist Davide Rebellin, who won a silver, have both been named by their associations.
The other cyclist was officially named as Stefan Schumacher, a German who faces a lifetime ban from the sport for a repeat offence.
Weightlifter Yudelquis Contreras was identified by the Dominican Olympic Committee as testing positive. Cera is an advanced version of the endurance-enhancing hormone EPO.
Ramzi, who used to compete for his native Morocco and still trains there, won Bahrain’s first ever track and field gold medal in Beijing last August. He also won the 800m and 1500m races at the 2005 World Championships in Helsinki.
The B sample of Ramzi will be tested in France on June 8 when he faces an IOC hearing. If he is stripped of his Olympic title, Kenya’s Asbel Kipruto Kiprop would be upgraded to gold, Nicholas Willis, of New Zealand, to silver and French man Mehdi Baala to bronze.
If Rebellin is disqualified, Fabian Cancellera, of Switzerland, would be awarded his silver medal and Alexander Kolobnev, of Russia, would get the bronze.
The IOC has not officially named any of the athletes or their sports.
Rashid and Rebellin will also be stripped of their medals and banned for two years if a supplementary B sample is also positive.
They were caught under a new rule allowing blood and urine samples to be stored for eight years after Games for retesting as detection procedures improve.
The International Olympic Committee (IOC) said it had conducted 948 retests of samples, mainly in endurance events where blood doping is of benefit. There were seven positive results involving six athletes.
The athletes were found to have taken Continuous Erythropoiesis Receptor Activator (CERA), the new generation of erythropoietin (EPO) that stimulates the production of oxygen-rich red blood cells.
Rwanda’s leading runner Dieudonne Disi was among the tested athletes at the Beijing Games and his results have never been revealed.