The Winston-Salem Journal has a good intro on the dangers of radon gas seeping into your house, how to test for it, and what to do about it it’s found. A sample:
You can’t see it, smell it or taste it, but one in 15 American homes contains high levels of radon, the naturally-occurring radioactive gas that is the leading cause of lung cancer for non-smokers.
This is the national average; many areas have significantly higher rates. Health agencies throughout the United States, including The American Lung Association, Centers for Disease Control and National Cancer Institute, all agree that radon is a national health problem.