OBJECTIVE: Physicians may prescribe buprenorphine for opioid agonist maintenance treatment outside of narcotic treatment programs, but treatment guidelines for patients with co-occurring cocaine and opioid dependence are not available. This study compares effects of buprenorphine and methadone and evaluates the efficacy of combining contingency management with maintenance treatment for patients with co-occurring cocaine and opioid dependence. METHOD: Subjects with cocaine and opioid dependence (N=162) were provided manual-guided counseling and randomly assigned in a double-blind design to receive daily sublingual buprenorphine (12-16 mg) or methadone (65-85 mg p.o.) and to contingency management or performance feedback. Contingency management subjects received monetary vouchers for opioid- and cocaine-negative urine tests, which were conducted three times a week; voucher value escalated during the first 12 weeks for consecutive drug-free tests and was reduced to a nominal value in weeks 13-24. Performance feedback subjects received slips of paper indicating the urine test results. The primary outcome measures were the maximum number of consecutive weeks abstinent from illicit opioids and cocaine and the proportion of drug-free tests. Analytic models included two-by-two analysis of variance and mixed-model repeated-measures analysis of variance. RESULTS: Methadone-treated subjects remained in treatment significantly longer and achieved significantly longer periods of sustained abstinence and a greater proportion drug-free tests, compared with subjects who received buprenorphine. Subjects receiving contingency management achieved significantly longer periods of abstinence and a greater proportion drug-free tests during the period of escalating voucher value, compared with those who received performance feedback, but there were no significant differences between groups in these variables during the entire 24-week study. CONCLUSIONS: Methadone may be superior to buprenorphine for maintenance treatment of patients with co-occurring cocaine and opioid dependence. Combining methadone or buprenorphine with contingency management may improve treatment outcome.