Shot put champion Irina Korzhanenko of Russia has been stripped of her gold medal and thrown out of the Games after failing a drugs test.
Korzhanenko tested positive for the steroid stanozolol after Wednesday's competition, and the backup B sample confirmed the initial finding.
She is the first athlete in Athens to lose an Olympic title through doping.
Cuba's Yumileidi Cumba Jay takes gold, Germany's Nadine Kleinert silver and Russia's Svetlana Krivelyova bronze.
Since two of their cross-country skiers were stripped of gold medals at the Winter Olympics in 2002, Russia have stepped up their efforts to clean up their team with random testing.
Russia's anti-doping chief Nikolai Durmanov told reporters on Monday: "We didn't want to repeat Salt Lake City but now we have a new Hiroshima.
"It was a great surprise because the basic priority in preparing for the Olympics was to ensure we had a clean team.
"We very much hoped that such a concentrated system of doping control would lay the ghost of Salt Lake City.
"Unfortunately we were mistaken in this hope."
The shot put competition was held at Olympia, the birthplace of the Olympics, and was meant to be a showpiece of the Games.
Korzhanenko, who dominated the competition, was stripped of the 1999 World Indoor title for drugs offences.
She was handed a two-year suspension and missed the Sydney Games in 2000.
Uzbek women's shot putter Olga Shchukina was expelled from the Games on Friday after failing a drugs test.
And Yanina Korolchik of Belarus, Olympic champion in Sydney, is currently serving a drugs ban.
If Korzhanenko is disqualified, the gold would go to Cuba's Yumileidi Cumba Jay.
The news came on the same day that Greek weightlifter Leonidas Sampanis was stripped of his bronze medal.
Sampanis tested positive for twice the allowed amount of testosterone.