This study used reinforcement principles to investigate some procedures for helping a 4-year-old Mexican-American girl establish peer contact in a Head Start class. Although Diane was healthy and intelligent, she had a low rate of attendance at school and spent most of her time there in isolation. The first procedure employed in the study was the controlled use of adult social reinforcement. A teacher was supposed to go to, talk to, smile at, touch, and praise Diane for participating in peer interaction. Due to Diane's impoverished peer-play repertoire, however, there were very few responses to reinforce and other procedures had to be tried. The adults next structured play situations to include Diane and gave her other prompts intended to lead to peer interaction that could be reinforced. As a result of this procedure, peer contact was markedly increased and prompting was subsequently phased out. It was also seen that the prompting-reinforcing process could be used to increase certain classes of behavior (such as verbal or nonverbal). In the final phases of the study, a rise in spontaneous, nonverbal behavior was seen and Diane's attendance at class became more regular. Behavior modification principles were therefore judged to be effective in remedying the subject's isolate behavior. (MH)