In the last decade, 13 Drug Counselling Units (DCUs) have been established in Norwegian prisons. These units are to offer prisoners with substance use problems coordinated treatment and rehabilitation so they can better cope with their problems during imprisonment and after release. Key means in achieving these goals are to establish inter-agency collaboration between the prison service and the specialist health services. Psychologists, social workers and prison officers from these institutions are to form an inter-professional team in the collaborative process. This study explores the challenges these occupational groups face when they collaborate within this organizational frame. The results show that the occupational groups experience two of the same types of challenges, but that they respond differently to them. The pattern of responses impacts collaboration, both in positive and negative ways. However, all occupational groups endeavour to maintain a high standard within the institutional framework provided by the Norwegian prison system. This article discusses how the responses of the occupational groups in the collaborative processes in the DCUs are influenced by their affiliation to the DCUs, as well as the system of management and professional logic.