Buprenorphine is undergoing clinical trials for the treatment of opiate addiction. Although the abuse liability of sublingual buprenorphine is low, reports of intravenous abuse have appeared. This study describes the physiologic and subjective effects of intravenously administered buprenorphine and naloxone given alone and in combination to methadone-maintained patients (40-60 mg/day). On four separate occasions at least 1 day apart, 6 subjects were administered either 0.2 mg buprenorphine, 0.1 mg naloxone, 0.2 mg buprenorphine and 0.1 mg naloxone in combination, or placebo. One male subject quit the experiment after three sessions because of excessive opiate withdrawal. Buprenorphine produced no significant physiologic or subjective effects. Naloxone produced marked opiate withdrawal symptoms. Buprenorphine in combination with naloxone produced characteristic physiologic and subjective opiate antagonist-like symptoms and signs. The parenteral abuse potential of the buprenorphine and naloxone combination is discussed.