As part of its research program to study the late effects of radiation in survivors of the atomic bombs, the Atomic Bomb Casualty Commission (ABCC) in conjunction with the Japanese National Institute of Health (JNIH), conducts biennial medical examinations on the selected population which comprises the ABCC-JHIN Adult Health Study sample. The patients herein described as Groups 1 and 2 were selected from among those examined in Nagasaki who had had a hemoglobin value of less than 11.0 g/100 ml at examination 2 years previously and who had responded to iron therapy sufficiently to justify a diagnosis of iron deficiency anemia. Almost all were women of child bearing age. The effect of iron therapy on the level of serum B/sub 12/ was investigated. Of 58 patients so studied, 46 showed some rise in post-treatment levels of B/sub 12/. This is evaluated as indicating that gastric secretion of intrinsic factor is depressed in the majority of iron deficient patients.