1. Observations on seventy-five established cases of leukemia occurring in people exposed to atomic bomb radiation are presented.
2. These data indicate a great increase in the incidence of leukemia among atomic bomb survivors due to a single massive exposure to ionizing radiation.
3. The leukemogenic effects of radiation are manifested equally in both sexes and at all age levels represented in this series.
4. The striking preponderance of chronic myelogenous leukemia compared to chronic lymphatic leukemia has been noted in exposed individuals but it is pointed out that chronic lymphatic leukemia is comparatively rare among the Japanese.
5. Cases of leukemia are still appearing in atomic bomb survivors. However, since 1950 there has been a steady decline in the number of cases.