Buprenorphine is a partial mu opioid agonist with demonstrated efficacy in the treatment of opioid dependence. One potential advantage of buprenorphine over full mu opioid agonists is its reported low physical dependence profile. This study systematically examined physical dependence produced by maintenance with a clinically relevant dose of buprenorphine using antagonist challenge procedures. In this residential laboratory study, eight opioid-dependent volunteers maintained on 8 mg/day of sublingual buprenorphine were each challenged on independent occasions with placebo, i.m. naloxone (0.3, 1.0, 3.0 and 10.0 mg/70 kg) and p.o. naltrexone (0.3, 1.0 and 3.0 mg/70 kg) 14 hr after their daily buprenorphine dose using a repeated measures, cross-over design. Both naloxone and naltrexone precipitated time- and dose-dependent withdrawal, as evidenced by changes in subject-rated, observer-rated and physiological measures. Significant precipitated withdrawal occurred at 3.0 and 10 mg/70 kg i.m. of naloxone and 3.0 mg/70 kg p.o. of naltrexone. These results indicate that buprenorphine maintenance produces physical dependence and that i.m. naloxone and p.o. naltrexone produce equivalent effects in withdrawal precipitation under these conditions. Findings have implications for selection of antagonist doses for use in formulating combination agonist/antagonist medications and for use in transition of drug abusers from buprenorphine to antagonist maintenance therapies.