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, in humans. ionizing radiation is carcinogenic and leukomogenic This conclusion is supported by numerous evidemiologic Studies conducted among human populations Giversity 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, these studies have demonstrated a preponderance of a specific histologic type of cancer, viz small cell undifferentiated carcinoma, when compared to the general population. Epidemiologic studies of the survivors of the atomic bomb explosians at Hiroshima and Nagasaki provide reliable data on the carcinogenic effects of whole body exposure to camma rays and neutrons. Among those individuals, an excess of lung, thyroid and breast cancer, as well as leukemia, 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.