The efficacy of a rapid detoxification schedule (8 to 10 days) with clonidine or methadone was evaluated in 30 patients addicted to heroin. The dose of study drug was preestablished according to the subject's weight and the amount of opioid consumption, and the total daily dose was reduced by approximately 15% during the study. All subjects completed the detoxification program and stayed in the hospital for at least 12 days. Clonidine and methadone therapies proved to be highly effective. There was a marked reduction in anxiety during opioid detoxification, although subjects' experiences differed according to the drug used. On the day of discharge, subjects who had received methadone still had attenuated withdrawal symptoms, whereas there were no such symptoms in the clonidine group. Muscular aching, flatulence, and daily drowsiness were more common among subjects in the methadone group, while subjects in the clonidine group had more sleep disturbances and weeping. Syncopal episodes and bradycardia occurred more frequently in the clonidine group.