According to tentative but widely accepted standards, any human fetus exposed to 10 rads or more during the first 6 weeks of pregnancy should be therapeutically aborted to avoid the possibility of a mentally and physically retarded child. Abnormalities of the brain are the most frequently cited radiation effects after prenatal exposure. Due to significant species differences in biological dose-response effects, extrapolation concerning early pregnancy low-dose effects on more subtle sensory-cognitive-motor functions and physical retardation are most likely verifiable only in diurnal primates which are of the same taxonomic order as man. The major objectives of this research program are: 1) Examine the effects of 10r and 100r whole-body gamma radiation exposure at 30 days of gestation on sensory-cognitive-motor behavior, neurochemistry and morphology in different laminae of the striate, somatosensory and motor regions of the cerebral cortex, the retina, cerebellum, hippocampus and hypothalamus of the squirrel monkey. 2) Evaluate the repair of and prospects for recovery of the neurological, behavioral, neurochemical, morphological and hematological alterations from 5 to 365 and 730 days of age after the prenatal exposure to ionizing radiation with special emphasis on delayed loss of neurons, the maintenance and possible repair of the remaining neurons in different laminae of striate, somatosensory, motor and associated regions of the cerebral cortex, the retina, cerebellum, hippocampus and hypothalamus of the squirrel monkey.