This study compares the withdrawal responses of methadone and heroin addicts during a ten-day in-patient detoxification programme with methadone. Contrary to suggestions in the literature, the methadone group reported more severe withdrawal symptoms during both the acute withdrawal phase and the recovery phase. There were no differences between the two groups in onset or duration of symptoms. Whereas there may be reasons to favour methadone as a maintenance drug, its use may lead to difficulties during withdrawal.