This complementary project draws subjects from two studies investigating contingency-management (CM) based treatments "Behavioral Treatment of Adolescent Marijuana Abuse" (DA015186), and "Family Based Contingency Management for Adolescent Alcohol Abuse" (AA016917). Both trials compare a unique CM intervention that involves an abstinence-based reinforcement program to a standard, state of the art cognitive behavioral intervention. Analyses would be performed separately for the two samples, with hypotheses tested first using the Marijuana sample, and assessed for replication/specificity using the Alcohol sample. The proposed project would explore novel neurobiological predictors of response to CM interventions.