The efficacy of clonidine, methadone, and guanfacine in rapid detoxification of heroin inpatients was assessed in a randomized controlled clinical trial. Signs and symptoms of abstinence and of side effects were analysed in 90 heroin addicts successfully completing a 12-day inpatient trial. All patients fit DSM-III criteria for opioid dependence, the age range being 18 to 36 years. All three drugs were effective in controlling abstinence; however, the course of abstinence was different in the methadone group as compared to the adrenergic agonists, the latter showing limitations in their ability to suppress withdrawal manifestations. While mean number of withdrawal signs and symptoms was significantly lower during days 2 to 5 in the methadone group (p less than 0.01), adrenergic agonists were slightly more effective at the end of the trial. Incidence of side effects was closely related to the dose administered. Hypotensive action of adrenergic agonists was more marked in orthostatic position. The present results suggest that methadone is superior to adrenergic agonists. Between these drugs clonidine appears to be less effective than guanfacine in controlling some withdrawal manifestations, and causes more side effects, mainly of cardiovascular nature.