The national study on medically controlled prescription of narcotics (heroin, morphine and intravenous methadone) was evaluated and a report on the main findings is made available, based on the main study and a number of additional special studies. The study with an intention-to-treat design includes data on 1035 probands. They received treatment following a uniform study protocol in 17 out-patient clinics and 1 penitentiary. The attribution of substances varied however (2 double-blind studies, 3 randomisation studies, the rest followed an individual indication). Intravenous heroin was well accepted and superior to intravenous morphine and methadone concerning compliance (reduction of illegal drug use) and retention, due to less negative side-effects. Dosages were stabilised, no lethal overdose occurred. The study documented significant improvement in health and social status of participants, especially in a reduction of depressive and anxiety states, of contacts with the drug scene and of illegal activities and prostitution. Half of those who left treatment proceeded to detoxification or methadone maintenance. Mortality, to a large extent due to infectious diseases acquired before participation in the study was by 1 % of the cohort per year. A continuation of this treatment approach is recommended for chronic and marginalised heroin addicts who failed in other treatment modalities. Similar conditions and safety controls as established for the study should be applied.