IOC president Jacques Rogge has claimed that positive doping cases will occur at this year's London Olympics.
However, the Belgian insists that "everything that is humanly possible" has been done to prevent such cases.
"Let's not be naive, there is a possibility of positive cases," Rogge told BBC Sport. "There have been positive cases in each of the Olympic Games since we started testing.
"There is doping but what I can say is everything that is humanly possible has been done in London to minimise as much as possible the trend of doping."
The London Games start on Friday, July 27.