This study will evaluate the efficacy of an exercise-based contingency management (CM) intervention. A total of 120 substance abusing patients in intensive outpatient treatment will be randomly assigned to one of two conditions: (a) standard care plus CM for completing goal-related activities not related to exercising (e.g., improving work, family, or transportation issues), or (b) standard care plus CM for completing exercise-related activities. Compared to those receiving goal-related CM activity contracting, it is expected that those in the exercise CM condition will participate in more physical activities and develop greater strength and flexibility, decrease drug use, reduce HIV risk behaviors, lessen depressive symptoms, and improve health indices.