Rats reared from weaning in social isolation made more lever presses than controls on an alternating two-lever DRL schedule of reinforcement, and obtained fewer rewards. Isolates showed an increased tendency both to anticipate reward on the correct lever, and to perseverate on the lever which last gave reward, but their anticipatory deficit was relatively more marked. It is suggested that isolates act as if under an effectively higher level of food motivation. Measurement of home-cage food intake showed that the normal day-time depression of food intake was less marked in isolates than in socially-grouped animals.