Discus champion Robert Fazekas has been stripped of gold for "refusing or failing to admit a urine sample".
Fazekas won the European title in Munich two years ago
The International Olympic Committee confirmed the Hungarian has been expelled from the Games.
Lithuanian Virgilijus Alekna has now been awarded gold, Hungary's Zoltan Kovago takes silver and Estonian Aleksander Tammert gets the bronze.
Belarus high jumper Aleksey Lesnichiy was also expelled for testing positive for a banned anabolic steroid.
Fazekas had won the gold medal with a throw of 70.93m in Monday's final.
"Under the IOC anti-doping rules Fazekas is disqualified from the men's discus, is not awarded the gold medal and is excluded from the Games," an IOC statement said.
"Whoever came second wins. He only provided 25 milligrams (of urine) and the minimum is 75."
An IOC source had earlier said Fazekas had been caught trying to switch his urine sample in dope testing following Monday's final.
The 29-year-old is the reigning European champion and won silver at last year's World Championship.
Fazekas is the second athletics gold medallist to forfeit their title at the Athens Games.
Irina Korzhanenko of Russia was stripped of her women's Olympic shot put gold on Sunday after testing positive for a steroid.
Belarussian Lesnichiy, who failed to qualify for the high jump final, was thrown out of the Games after
testing positive for clenbuterol, a banned steroid.
The departure of Fazekas and Lesnichiy means a record 16 competitors have now been expelled from the Athens Olympics over drugs.