Recent preclinical and clinical studies suggest that buprenorphine, an opioid mixed agonist-antagonist, may be useful for the treatment of dual dependence on cocaine and opiates. This report describes an inpatient clinical evaluation of the safety of buprenorphine alone and in combination with single doses of cocaine and morphine. Twenty subjects with a DSM-III-R diagnosis of concurrent cocaine and opioid dependence were randomly assigned to maintenance treatment with single daily doses of 4 or 8 mg of sublingual buprenorphine for 21 days. Side effects and vital signs were evaluated every day once every 8 hours and for 2 hours after daily buprenorphine administration. The physiologic effects of a single-blind challenge dose of cocaine (30 mg intravenously), morphine (10 mg intravenously), and intravenous saline placebo were measured before and during buprenorphine maintenance. Before buprenorphine maintenance, subjects underwent methadone detoxification followed by a 9-day drug-free period. Three baseline single-blind challenge dose studies were conducted on study days 7, 8, and 9 during the drug-free period. Cardiovascular responses to cocaine and to morphine were equivalent under drug-free and buprenorphine maintenance conditions. Respiration and temperature changes in response to cocaine were also equivalent before and during buprenorphine maintenance. Respiratory rates were slightly lower after morphine administration during maintenance on 8 mg of buprenorphine, but this was not statistically significant. Mild opioid agonist-like side effects were reported during buprenorphine induction and maintenance. These included headache, sedation, nasal discharge, abdominal discomfort, and anxiety. Most opioid agonist side effects decreased within 12 to 14 days. An electrocardiogram and blood chemistry measures were normal before and during buprenorphine maintenance. These data suggest that daily maintenance on buprenorphine is not associated with adverse side effects or toxic interactions with a single acute dose of intravenous cocaine or morphine.