Nearly 600 homes from across the country have been found to have high levels of cancer-causing radon gas so far this year.
This is the highest number identified in any period since the national radon measurement programme began.
Radon is the second biggest cause of lung cancer after smoking and is linked to up to 200 lung cancer deaths each year in Ireland.
According to the study, certain homes in Lisdoonvarna, Clonmel, Ballymote and Tralee had more than 10 times the acceptable level of radon gas.
Senior scientist with the Radiological Protection Institute of Ireland (RPII) David Fenton said these areas had been known to be "radon black spots".
A total of 4,296 homes were measured by the RPII for radon gas between Jan 1 and August 30 this year - the highest number ever measured in a similar period. Of these, 597 were above the acceptable level of radon.