The number of homes at risk from radon gas has increased by more than one-third, according to the Environmental Protection Agency.
The agency has published new radon maps shows the areas most at risk from the gas, which causes hundreds of lung cancer cases every year.
You can check the level of risk in your home using the EPA Eircode map search.
Around 170,000 homes around the country are now predicted to be at risk - an increase of 45,000 on the last estimate, carried out in 2002.
EPA Director Michéal Lehane said the new maps show that large parts of the country - particularly in Munster and Connacht - are at increased risk.
"Radon is a serious public health hazard," he said. "The new maps combine thousands of radon measurements with detailed geological information and are a significant revision of the previous map from 2002.
"More importantly, the new maps make it easy for everyone to find out the radon risk in their local area using the Eircode search on the EPA website.
"We urge people to test for radon as this is the only way of protecting you and your family from this cancer-causing gas."
Radon is a radioactive gas that comes from the decay of uranium in rocks and soils.
Exposure to radon is linked in up to 350 cases of lung cancer in Ireland each year. It has no smell, colour or taste and can only be detected using special equipment.
While the gas quickly dissipates in the open air, it can accumulate to dangerously high concentrations when it enters enclosed spaces.
The EPA said radon testing is simple and inexpensive and where they are needed, radon reduction measures are also straightforward.
The agency provides a list of registered radon measurement services.
It also publishes a list of registered contractors who offer radon remediation services where needed.
The EPA radon team is also available to answer your queries at email@example.com or 1800 300 600.