This study used the behavioral contrast paradigm to assess the excitatory and inhibitory capabilities of young infants. Behavioral contrast is described as the phenomenon whereby the rates of responding in the presence of two stimuli, both of which were previously associated with reinforcement, change in opposite directions when only one of them becomes associated with the reinforcer. In the study, 20 infants 93 to 120 days old were trained on 2 days to produce rotation of an overhead mobile via right footkicks in the presence of two visual cues. After achieving a criterion of stable responding on a third day, one group of infants receiVed alternating 30-second periods of reinforcement and nonreinforcement with one cue signalling each component of the reinforcement schedule. These infants dramatically increased their rate of response when reinforcement was available; however, the expected corresponding response decrease during nonreinforcement periods was not evidenced. Control infants, who continued to receive continuous reinforcement throughout the third-day session, did not change their rate of response from criterion. All infants returned to a similar response rate on a fourth day when reinforcement was continuously available for both groups. Results indicated that young infants manipulated their visual environments in relation to changes in reinforcement density from previous reward experiences. Finally, the ability of young infants to rapidly inhibit previously reinforced motoric responses was discussed. (Author/CM)