BEIJING — Olympic officials have conducted more than 600 doping tests in the two weeks before the opening of the Beijing Games, and none of the samples have come back positive, the International Olympic Committee medical director said Thursday.

Patrick Schamasch said about 650 urine and blood controls had been carried out at various locations in China and abroad, including the athletes' village in Beijing and training sites in Singapore, Hong Kong and Britain.

"There have been no adverse results so far," he said.

The Olympic testing program began on July 27 with the opening of the village. Athletes can be tested at any place and at any time.

A record total of 4,500 tests will be conducted through the end of the Aug. 8-24 games, compared to 3,600 in Athens in 2004.

There were 26 positive doping cases in Athens. IOC president Jacques Rogge on Thursday said that based on mathematical probabilities, there could be between 30 and 40 positives in Beijing.