The effects of maternal agitation, induced by exposure to bright light, upon fetal well-being were studied in pregnant rhesus monkeys at 139 to 148 days of gestation. Fetuses were classified as "healthy" or "asphyxiated" according to their initial acid-base state. Following variable periods of maternal excitement, a decrease in heart rate and arterial oxygenation was seen in all fetuses. Recovery occurred more rapidly in the healthy group, after maternal sedation was achieved, either by removing the stimulus or by additional administration of pentobarbital, 5 to 20 mg. intravenously. The beneficial effects of meternal sedation on the fetus have thus been demonstrated.