Buprenorphine, an opioid mixed agonist-antagonist, is a potent analgesic that appears to be effective for the treatment of opiate abuse. Recent preclinical studies have shown that buprenorphine also significantly reduces cocaine self-administration by rhesus monkeys for periods up to 120 days. This unexpected finding has led to clinical trials to evaluate buprenorphine's effectiveness for the treatment of dependence on both cocaine and opiates, as defined by DSM-III-R criteria. Buprenorphine's safety in combination with cocaine and opiates and its effects on electroencephalographic sleep patterns and regional cerebral blood flow were evaluated during inpatient studies. Buprenorphine (4 or 8 mg/day given sublingually) did not accentuate the cardiovascular and respiratory changes induced by an acute challenge dose of cocaine (30 mg given intravenously) or morphine (10 mg given intravenously) alone. In an outpatient open trial, buprenorphine significantly reduced both opiate and cocaine abuse by patients who had abused these drugs for more than 10 years. Most of these patients had failed in other drug abuse treatment programs. Reports of needle sharing also decreased significantly, and no patient tested positive for human immunodeficiency virus (HIV). The apparent safety and effectiveness of buprenorphine, combined with a high level of patient acceptance, led the Food and Drug Administration to grant a compassionate extension of the approved period for outpatient buprenorphine treatment from 26 to 52 weeks. Clinical trials of buprenorphine are ongoing. Possible mechanisms underlying buprenorphine-cocaine interactions are now under investigation.