Patterns of learning by five infants with Down's syndrome (3.5 to 12.5 months old) were studied. The children were visited at home 2 to 3 times per week for periods ranging from 1 to 8 months. Two of the children were reinforced for pulling a string attached around their wrist. Consequences included tape recordings of music or their mother's voice, a colored light, and other stimulating materials. The type of reinforcement was changed when the response fell below the baseline rate. The other three infants were reinforced for kicking. Visual attention and responses to the manipulands and consequence were recorded. After the child had achieved a stable rate of responding on the operative response, the contingencies were reversed. All of the children showed rapid differentiation of the reinforced pulling response from the nonreinforced kicking response. However, the reinforced kicking response showed rapid differentiation only for the two children who learned the arm response first. These data suggest that the establishment of the generalized expectancy of control over the environment is more efficient if one begins with contingencies for movements which are most "prepared" for the individual child. Overall, the results suggest that handicapped children under 1 year of age can learn through simple contingencies of reinforcement. However, the patterns of acquisition appear to be somewhat different for different children. (SEW)