Mortality to 60 days following exposure to60 Co γ-radiation (bilateral, whole-body; 10 min exposure time) has been studied in 387 male and 273 female purebred beagles exposed at various ages from the late fetal stage to adulthood.${\rm LD}_{50/60}$ values in males and females respectively were estimated to be: 55 day fetus, 324 and 295 R; 2 days post partum, 385 and 408 R; 15 days, 378 and 355 R; 35 days, 322 and 278 R; 63 days, 287 and 270 R; 70 days, 290 and 272 R; and in 1.5-2 yr-old males and 4-6 yr-old females respectively, 316 and 278 R (midline, in-air exposure). Except in animals irradiated prenatally, most deaths occurred 15-20 days post exposure. Bone marrow damage appeared to predominate.

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