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The athletes, from Russia and Belarus, include three gold and two silver medalists. Among them was Nadzeya Ostapchuk of Belarus, a shot putter who placed first. She had also been stripped of her gold medal at last summer's London Olympics after testing positive for an anabolic steroid after her event.

The hammer throw champions in 2005, Ivan Tsikhan of Belarus and Olga Kuzenkova of Russia, were also found to be doping, the international federation, I.A.A.F., said. The other athletes cited were Andrei Mikhnevich of Belarus (shot put), Vadim Devyatovskiy (hammer) of Belarus and Tatyana Kotova of Russia (long jump).

"The I.A.A.F.'s message to cheaters is increasingly clear that, with constant advancements being made in doping detection, there is no place to hide," the organization's president, Lamine Diack, said in a statement.

The I.A.A.F. did not say what banned substances were found in the re-examination. Antidoping officials keep samples for a minimum of eight years because that is the statute of limitations for retroactively banning an athlete for testing positive.

Officials said disciplinary procedures had begun against the six athletes, which could result in the stripping of their medals and suspensions from the sport.