Results of the study indicate that voucher-based reinforcement of negative urines and of treatment plan tasks showed no statistically significant effects on measures of retention or drug use relative to the standard treatment protocol. It was likely that punishment and contingent reinforcement (positive and negative) operating within the context of the Substance Abuse and Crime Prevention Act (SACPA) drug treatment court created an effect that overrode the potentially reinforcing effect of vouchers. Extensive research on contingency management (CM) interventions among drug abusers has resulted in substantial literature documenting the effectiveness of the approach. CM has been established as assisting drug treatment participants by reinforcing continuous abstinence during treatment. The use of voucher-based contingent reinforcement of activities consistent with treatment goals has been evaluated within several drug treatment programs. However, to test its effectiveness in the context of the criminal justice system, this study assessed a 26-week voucher-based intervention to reinforce abstinence and participation in treatment-related activities among substance-abusing offenders court referred to outpatient treatment under drug diversion legislation, California's SACPA. Tables, figures, note, and references