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Six monkeys subjected to forelimb deafferentation on day of birth (two blinded and four not blinded) spontaneously developed use of the affected limbs for support of body weight, ambulation, and clasping objects. The sighted animals also used them for climbing and reaching toward objects. Thumb-forefinger prehension did not emerge spontaneously but could be brought into existence through training. In another series of experiments, 5 of 11 monkey fetuses, exteriorized two-thirds of the way through gestation and given forelimb deafferentation, survived through caesarian delivery and at least 5 months of infancy. Although all were quadriparetic due to postoperative mechanical deformation of the cervical region, they were able to use the affected limbs to make postural adjustments and for standing and rudimentary ambulation. The results indicate that, after birth, neither spinal reflexes nor local somatosensory feedback and vision are necessary for the development of most types of movement performed by the forelimb musculature in monkeys. Continuance of the prenatal research should permit determination of the role of somatic sensation in the intrauterine development of behavior.