The operator of Japan's crippled nuclear power plant said two workers have exceeded a radiation exposure limit for men.
Tokyo Electric Power Co said the two control room operators were the first men to surpass the government-set limit.
Dozens of other workers are being tested further.
The two men are not showing any immediate health problems from their exposures due to working at the plant where the March 11 quake and tsunami knocked out power and cooling systems.
Tepco has been criticised for not fully disclosing the extent of radiation exposures by the plant workers or their working conditions.
The government raised a conventional exposure limit for men to confront the emergency soon after the disasters struck.