The process of achieving a high retention rate of subjects in a 12-month prospective study of intravenous heroin users in Sydney, Australia is presented. Self-referred heroin users were compared with heroin users from a court diversion programme. The retention rates throughout the prospective study interview schedules were high, ranging from 69 to 83% of the original sample. No statistical differences were detected between the proportions located at each interview, indicating a high retention rate was maintained despite the passage of time. It is argued that contact with State services, i.e. Methadone Maintenance Programmes and the legal system, particularly the prison service, contributed to this high maintenance. It is speculated that the effectiveness of location strategies reflect prominent characteristics of the populations studied.