ALTHOUGH RADON IN INDOOR AIR has been widely recognized as a significant public health problem only since the 1970s, radon has been linked to excess lung cancer in underground miners since the early decades of this century. As long ago as the 1500s, Agricola described unusually high mortality from respiratory diseases among underground metal miners in the Erz Mountains of eastern Europe, a region presently encompassed by Germany and Czechoslovakia . The disease, termed “bergkrankheit,” probably represented lung cancer, silicosis, and tuberculosis, common diseases of underground miners. In 1879, Harting and Hesse reported autopsy findings in miners of Schneeberg in Germany that documented an occupational hazard of lung cancer, although they did not identify the disease as primary cancer of the lung. Early in this century, further pathological studies showed that the miners developed primary carcinoma of the lung .