The International Olympics Committee, in a release Wednesday, said analysis of stored samples taken more than eight years ago revealed the use of banned substances. The results led to the IOC requesting return of the medals.
The athletes are Bilonog, who won the shot put for Ukraine; Russia women's shot put bronze medalist Svetlana Krivelyova; Belarus hammer throw silver medalist Ivan Tsikhan; and Belarus women's discus bronze medalist Iryna Yatchenko.
The IOC keeps samples for eight years after each Olympic Games to allow for testing as technologies and detection methods improve. An IOC release said further testing of samples from the Athens Games came "as a result of targeted testing based on intelligence and new methods."
One pending case remains from this series of retests, the IOC said.
The IOC said Bilonog and Krivelyova tested positive for oxandrolone metabolite while Tsikhan and Yatchenko were determined to have used methandienone metabolite. Both are anabolic steroids.