Olympic athletes using drugs were warned "we are going to catch you" on Saturday after the London Games were hit by their first doping case on the opening day of full competition.
The International Olympic Committee (IOC) said the case of Albanian weightlifter Hysen Pulaku, who tested positive for a banned steroid in London this week, showed drug cheats will be found out.
"Of course, it is always a sad day when a cheating athlete is caught. We hope there will be no more, but the message is very clear: if you are doping we are going to catch you," said IOC spokesman Mark Adams.
"There are going to be 5,000 tests during these Games and all the medallists will be questioned and no one can think that they can get away. It's disappointing."
More than a dozen other athletes have already been expelled for pre-competition doping offences, but Pulaku, 19, is the first to fail a test since arriving for the Games.
The 77kg contender tested positive for stanozolol in London on July 23, becoming the 10th weightlifter caught doping at an Olympics since 2000.
Two Turkish weightlifters have also been kicked out of the London Games over pre-competition tests.
European silver-medallist Fatih Baydar and Ibrahim Arat were expelled from Turkey's squad after failing dope tests on July 7.
Among the other pre-Games doping casualties were Morocco's Mariem Alaoui Selsouli, one of the favourites for the Olympic women's athletics 1500m gold medal, who failed a test for a banned diuretic.
World anti-doping chiefs have unveiled a new test for human growth hormone, with a detection window of weeks rather than hours, which they hope will snare drug cheats at the Games.
A total of 15 athletes were caught doping at the 2008 Beijing Olympics, the most at a Summer Games since the IOC began outlawing drugs at the 1968 edition in Mexico City.
Doping tales at the Olympics are legion. This week, China's lead doctor at the Los Angeles, Seoul and Barcelona Games admitted testing hormones, blood doping and steroids on elite athletes -- but said other countries were doing the same.
"The United States, the Soviet Union and France were all using them so we did as well," Chen Zhanghao, who retired in 1992, told Australia's Sydney Morning Herald.
"So how can you condemn China but not the USA or Soviet Union?"