Physiological, cognitive, and emotional factors were examined throughout the treatment of a psychotic child. Heart rate, latency and accuracy in task performance, behavioral indices of stress (e.g., muscular tension, facial expression), and frequency of autistic mannerisms were measured concurrently. Both contemporaneous relationships and patterns of change suggested that autistic behaviors were organized and psychologically meaningful. Self-stimulation, conflict, and negativism (deliberate erroneous performance) occurred predictably, were intimately related, and were associated with specific patterns of heart-rate change. The changing function of self-stimulation across treatment and the centrality of negativism in this child's disturbance were discussed.