Differential response effectiveness is examined for patients during multiple episodes of metha done maintenance (MM) treatment. Subjects were 251 narcotics addicts who were divided into three groups based on their daily narcotics use pattern during their first two MM treatment penods: (I) a "stabilizing group"—showing no daily use for both periods, (2) a "cumulative group "—showing a lower level of daily use during the second period compared to the first, and (3) a "deteriorating group"—showing higher daily use during the second period. Behavioral measures for various narcotics-related variables were plotted over 4 time penods (pre-MM, during first MM, between first and second episodes, and during second MM) were compared. Results indicated several individual differences related to patients'response to multiple episodes of MM. Clinical, research, and policy implications are discussed.