Aims: To assess substance users' beliefs and the sources of these beliefs regarding methadone and buprenorphine and to examine how they choose between them. Design: Forty-two opiate-dependent patients seeking treatment chose between open label buprenorphine or methadone maintenance treatment. Prior to treatment patients completed a semi-structured interview or a self-completed questionnaire. Findings: Beliefs were based primarily on their own or other users' experiences. All patients chose their treatment. There was little difference between those choosing MMT and BMT in terms of their beliefs about the drugs, although the BMT group viewed methadone more negatively and buprenorphine more positively than the MMT group. Those choosing MMT appeared to do so on the basis of familiarity whereas those choosing BMT appeared to be attracted by their beliefs that it would block heroin more effectively, reduce craving, give less intoxication and be easier to stop taking. Conclusions: Opiate users rapidly become well informed about a new treatment when it becomes available. They rely more on their own and other users' experience than the information given by agencies. Choices between treatments are based more on individual perceived requirements than different beliefs.