evidence is not particularly helpful in deciding specific causation in any individual." Both of these statements are incorrect. First, it is well known that epidemiologic studies have documented that radiation not only causes cancer but also that radiation causes cancer of specific histologic type. In fact, there can be little doubt that, under a wide variety of circumstances, ionizing radiation is carcinogenic and leukomogenic in humans. This conclusion is supported by numerous epidemiologic studies conducted among human populations diversity of exposure to radiation. which have experienced a Epidemiologic studies of uranium miners exposed to alpha and gamma radiation have demonstrated a large excess of bronchogenic cancer. In addition, have demonstrated a preponderance of a specific these studies histologic type of cancer, viz small cell undifferentiated carcinoma, when compared to the general population. Epidemiologic studies of the survivors of the atomic bomb explosions at Hiroshima and Nagasaki provide reliable data on the carcinogenic effects of whole body exposure to camma rays and neutrons. Among those individuals, and breast Cancer, as well as leukemia, an excess of lung, thyroid has been demonstrated. This excess of leukemia was shown to be predominantly of the myelogenous and granulocytic type. Conclusive evidence that therapeutic radia- tion can be carcinogenic and leukomogenic comes from studies of patients irradiated for ankylosing spondylitis, thymic enlargement and gynecological disorders. In like manner, epidemiologic studies have shown that radiologists exposed to radiation have an excess of leukemia when compared to other physicians not so exposed.