Differential consequences were used to increase obedience and decrease aggressive behavior in a four-and-one-half year old boy. Treatment was conducted in the child's home by his mother.Traditional forms of child therapy attempt to modify problem behaviors by placing the child in an artificial environment where he interacts with a highly trained specialist. Treatment is usually based upon the assumption that deviant behaviors are symptoms of some underlying emotional disturbance, and treatment is designed to modify these hypothetical underlying causes. However, a learning theory approach suggests that both desirable and undesirable behaviors of the child are maintained by their effects upon the child's natural environment (Bijou and Sloane, 1966). If this is true, the most efficient way to modify deviant behavior may be to change the reactions of the natural milieu to that behavior.Differential social reinforcement and the use of a timeout from reinforcement have been successfully used to change children's behaviors in a nursery school setting (Harris, Wolf, and Baer, 1964; Sloane, Johnston, and Bijou, in press). In Wahler, Winkel, Peterson, and Morrison's (1965) report of the use of social reinforcement to modify children's problem behavior, the children's mothers, rather than a nursery school teacher, served as therapists. Under controlled laboratory conditions, each mother interacted with her child in specific ways on cue from the experimenter. Russo