Experimental modification of destructive and assaultive sibling interaction was carried out within the home environment. Two brothers (6 and 3 years old) were treated through token positive reinforcement techniques in an effort to improve their behavior towards each other. A "time out" from reinforcement procedures involved an isolation period for the sibling practicing destructive behavior. At first the program was carried on by the experimenter, who devised techniques to meet clinical and research needs as the study progressed. When the boys had shown sufficient improvement, the modification techniques were taken over by their mother, under the experimenter's guidance. The children's behavior changed markedly under the reinforcement system and was generalized to other times and situations, according to parental and teacher reports. While the investigators recognize that factors other than behavioral therapy (such as the 3-year-old's improved verbal facility) contributed to the behavioral improvement, they conclude that parents can use modification principles to change deviant behavior in their own children. (MS)