[en] Three related, but separate, studies are in progress. In the first, young adult beagles of both sexes are placed in the γ-ray field, to be kept there for duration of life at one of a number of daily exposure rates. In the second, young adult beagles are exposed in a similar fashion until they have accumulated predetermined amounts of total exposure ranging up to 4000 R, delivered at various daily exposure rates. They are then removed from the radiation field and kept for the rest of their lives to allow development of late effects attributable to radiation exposure. In the third study, pregnant beagles are irradiated, at one of four daily exposure rates, for all or part of their gestation periods, to produce an evaluation of the effects of continuous irradiation in the developing fetus. All of these studies are done by arranging dogs at various distances from a calibrated ⁶⁰Co γ-ray source, where they are irradiated during 22 hours of each day. The remaining 2 hours are used for animal care, maintenance, and clinical evaluation of the dogs. The combined results demonstrate that the cellular and organ systems of the dog respond predictably, and in a differential manner, depending on exposure rate. Exposure rates in excess of 17 R/day destroy the blood-cell producing elements of bone marrow and cause death, therefore, within 1 to 2 months. Minimally sublethal exposure rates to bone marrow (5-17 R/day), however, produce a very high (50-75 percent) incidence of anemia or myeloid leukemia. Furthermore, at exposure rates of 5 R/day or below, bone marrow appears to function in an essentially normal fashion, and causes of death appear, from preliminary data, to be related to degenerative disease and malignancies of other tissues