At a news conference on the eve of the opening ceremonies, IOC President Jacques Rogge used a historical reference to make a prediction on the number of drug cases he expected to come out of the Olympics.
There were 3,500 drug tests taken at the Athens Olympics four years ago, he said, and 26 of them were positive.
"So between 30 to 40 (positive tests are expected)," Rogge said. "If we have less, I'd be extremely glad because that would mean there would have been a deterrent effect."
Rogge said it was unrealistic to expect no positive tests in Beijing.
"There will always be criminality in society," he said. "You cannot imagine a society without laws, without prisons, without cops, without justice. It's exactly the same in sport. You have approximately 500 million people practicing competitive sport around the world. You don't have 500 million saints on Earth."