A meta-analysis was conducted on contingency management interventions in outpatient methadone treatment settings. The outcome measure of interest was drug use during treatment, as detected through urinalysis. The results confirm that contingency management is effective in reducing supplemental drug use for these patients. The analysis of behavioral interventions yielded an overall effect size (r) of 0.25 based on 30 studies. Significant moderators of outcomes included type of reinforcement provided, time to reinforcement delivery, the drug targeted for behavioral change, number of urine specimens collected per week, and type of subject assignment. These factors represent important considerations for reducing drug use during treatment.