The Ukrainian four-woman rowing team was stripped of its bronze medal on Thursday after one member tested positive for a banned drug, an IOC source said.
It was the fourth medal lost because of doping during the Athens Olympics.
A weightlifter from Hungary also was expelled from the games on Thursday for failing to provide a urine sample after his event, the International Olympic Committee said.
Zoltan Kovacs, who finished last in the 105-kg class, became the 10th weightlifter punished for doping.
Three medals have been stripped in the last four days because of doping violations. Hungary's Robert Fazekas lost his gold in the discus and Russian Irina Korzhanenko lost her gold in shot put.
The latest case involved a rower who evidently was unaware that she was taking a banned substance, the IOC source said.
Olena Olefirenko was part of Ukraine's four-woman crew that finished third in lightweight sculls on Sunday. Australia finished fourth and will now get the bronze. Germany won the gold and Britain took the silver.
Olefirenko got medication from a team doctor that contained a stimulant that is banned, the source said. Olefirenko reported that she took the drug when she was tested after the race, but didn't realize it was banned, the source said.
{{/usCountry}}Olefirenko got medication from a team doctor that contained a stimulant that is banned, the source said. Olefirenko reported that she took the drug when she was tested after the race, but didn't realize it was banned, the source said.
{{/usCountry}}If one member of a rowing crew fails a drug test, the entire crew loses the medal.