Over tha past 10 years drug treatment programmes have been exstensivly developed in Swedish prisons. Thsi article highlights how prison officers working in treatment wings think and act in relation to their professional role, their relations to the prisoners and the organisation of drug treatment within the prison. Data consists of interviews and observations from three Swedish prisons in different security categories. The study examines the significance of secdurity categorie, overall prison-staff culture, treatment wing culture, inmate gender and the treatment role and officers work identity in the treatment wings. The ways in which prison officers think and act depends on how their professional roles are defined at the different prisons. Definitins differ in regard to views on addiction, preferences fo the ways in which treatment should be performed and organized and ideas about how ideal levels of staff-prisoner interaction are best accomplished within the treatment context.