The monograph describes a systematic attempt to develop language behavior in a nonverbal autistic 4.5-year-old boy who was essentially unresponsive to environmental stimuli of any kind. The 45-session intervention focused on teaching him to attend, increasing his responsiveness to people, effecting discriminative responses to a variety of controlled auditory and visual stimuli, increasing the extent and rate of his vocal and nonvocal behavior, and increasing the control of his behavior by verbal commands. Principles of behavior modification were used in such activities as "tickling," various games in which the child's verbalizations maintain the action, and responding to his name and simple commands. The intervention resulted in an increase in the frequency and variety of his verbal and nonverbal behavior; his behavior is more under appropriate stimulus control; and people are more frequently sources of discriminative and reinforcing stimuli for him. He laughs, makes some sounds similar to those of others, responds to his name, pays attention, does simple tasks, and is generally more alert and responsive. (DB)