The spontaneous physical dependence of buprenorphine was assessed in opioid addicts who switched from heroin to sublingual or intravenous buprenorphine. Twenty-two patients were randomly assigned to double-blind administration of methadone (n = 11) or placebo (n = 11) for 13 days after abrupt withdrawal of buprenorphine. Methadone was administered according to four pre-established dosing schedules depending on the previous amount of daily consumed buprenorphine. No methadone-treated patient required modification of the therapeutic regimen, whereas eight of eleven placebo-treated patients needed treatment with methadone. Buprenorphine withdrawal syndrome was of opioid type, began somewhat more slowly, and showed a peak until day 5. The occurrence, time-course and characteristics of buprenorphine withdrawal syndrome make it necessary to reconsider the abuse potential of this analgesic.