Thirty-four drug addicts, aged 20 - 24 years, with a history of 4 - 8 years of intravenous heroin abuse, were randomly assigned either to a methadone maintenance treatment (MMT) (17) or to an untreated group (17). The untreated controls could not apply for entrance to the program until two years later. It was found that after two years 12 MMT patients had abandoned their drug habits and begun work, whereas 5 had recurrent drug abuse problems. Of the controls, one was drug-free and gainfully employed, 12 were continuously abusing heroin (3 of these had incurred potentially fatal diseases in consequence), 2 were in prison and 2 had diet. Two to seven years after their first visit to the Psychiatric Research Center 8 of the original control group have been accepted into the program. At present 19 (out of 25 admitted) are gainfully employed and no longer abusing drugs. Among the remaining controls 4 are dead, 3 are in prison, one in spite of a serious heart condition abuses heroin and one is drug-free. The rehabilitation rate was thus 76 per cent in the program as compared to 6 per cent among the control group. In addition, MMT obviously reduced the high morbidity and mortality rates found in a selection of heroin addicts who fulfilled the admittance criteria of the Swedish program.