Homes in Scotland at risk of a build-up of carcinogenic radon gas will be tested to assess the danger.
A map has been published showing the areas of Scotland that have the highest levels of the natural gas.
Radon is not considered dangerous unless in high concentrations with long-term exposure, when it can increase the risk of lung cancer.
Health secretary Nicola Sturgeon said: ‘The build-up of radon in houses can put health at serious risk and is estimated to cause between 100 and 200 lung cancer deaths in Scotland every year.
‘This new map identifies the areas of Scotland most affected and the measures announced by the Scottish government will assist those homeowners most at risk to get their properties tested.’
Anyone in an area where their house has a 5% chance or more of being above the action level will be entitled to a free test by the Health Protection Agency, with the scheme starting this summer and continuing until 2011.
Although 62,000 Scottish homes are located in Radon-affected areas, only 1,000 to 3,000 will have concentrations above the action level.