The use of contingent positive reinforcement and aversive procedures in reducing inappropriate behaviors in five autistic preschoolers was examined. Ss were reinforced for appropriate behaviors (including spontaneous eye contact and verbalizations, appropriate play, interaction, and direction following) and not reinforced for inappropriate behaviors (such as self stimulation, crying, echolalia, noncompliance, and aggression). Data were collected under four conditions in the clinic and under three conditions at home. Results revealed that treatment without aversives was inferior to results obtained with children who had received both reinforcement and contingent aversives early in treatment. A single spank on the thigh, bottom, or hand combined with a stern "no," used as a contingent aversive, resulted in rapid and dramatic decreases in five of the six targeted behaviors. Further, over a 4 to 6 month period, the suppressive effects of punishment were maintained, usually only with limited use of conditioned aversives. Findings suggested that contingent aversives may be an essential component of effective treatment for autistic children. Caution is advised to make sure that the environment provides opportunities for learning and reinforcement. (CL)