1. Hematologic findings in in utero atomic bomb irradiated and nonirradiated children of Hiroshima between the years 1950 to 1957 have been compared, and no changes peculiar to the irradiated group were found.
2. Despite several predisposing factors in Japan toward the development of iron deficiency in children, overt anemia was rare and distribution of hemoglobin levels was only slightly lower than those reported in American and European children.
3. Leukocyte levels, irrespective of age of the children, were found to be progressively falling in the children of Hiroshima, whether or not exposure to irradiation had occurred. Thus, by 1957 the values were distinctly lower than those reported for normal children in Japan and the United States. No cause for this change was apparent.