A method of behavioral control which utilizes nutritive sucking as the operant has been evolved in our laboratory. Using this technique we studied the role of arousal and learning in the development of environ- mental control over earliest feeding behavior. Few of the infants in our studies were able to coordinate their sucking behavior to arbitrary operant-discrimination schedules, but when the individual pattern of suck- ing was taken into consideration, some infants rapidly adapted to the reinforcement schedule. Data from various reinforcement schedules suggest that earliest mothering...