DURING THE LAST TWO DECADES, it has been well publicized that exposure to radon causes lung cancer. Radon, a naturally occurring radioactive gas, seeps into and accumulates inside buildings. Elevated indoor radon concentrations have been observed in all parts of the United States . A consensus of opinion on human carcinogenicity of radon has been well established from studies of uranium miners by national and international health organizations such as the World Health Organization's International Agency for Research on Cancer (IARC) , the Biological Effects of Ionizing Radiation (BEIR IV) Committee of the National Academy of Sciences , the International Commission on Radiological Protection (ICRP) , and the National Council on Radiation Protection and Measurement (NCRP) . Still, the magnitude of exposure to and risks due to radon are not fully recognized by the general public.