In a double-blind study carried out between 1972 and 1975 in Hong Kong 100 heroin addict volunteers were initially admitted to hospital for two weeks for stabilisation on 60 mg of methadone before being assigned at random to two groups: one group received methadone (range 30--130 mg, average 97 mg/day); those in the other group had their dose of methadone reduced at the rate of 1 mg/day and were then maintained on placebo. All subjects were provided with a broad range of supportive services. After thirty-two weeks 10% of the controls were still on treatment, compared with 76% of those receiving methadone. At the end of the three-year project, only 1 of the original 50 placebo subjects still turned up for treatment (2%), whereas the retention-rate (proportion still on treatment) for methadone subjects was 56%. Subjects who had dropped out of the study and were readmitted for methadone treatment under known conditions had the same retention-rate as the original treatment group.