More than 400 homes around the country have been identified with high levels of the cancer causing gas radon in the past 18 months.
According to figures from the Radiological Protection Institute, one home in Tralee, Co Kerry had 26 times the acceptable level.
The institute says that occupants were receiving the equivalent radiation dose of around 18 chest X-rays a day.
Ten other homes, five in Kerry, three in Galway and one each in Clare and Wexford were identified with radon levels more than 10 times the acceptable level.