This paper draws on qualitative case-study research to discuss the impact of managerialism on the work organisation of public sector health professionals in Australia. The case studies included 71 semi-structured interviews with a broad range of public sector health professionals (predominantly nursing and allied health professionals, with some doctors and managers). The data are used to examine the implications of managerialism for the organisation of professional (public) bureaucracies. The findings show that while health professionals were able to exert their agency to influence managerial processes, the incorporation of managerial strategies into professional practice placed constraints upon professional autonomy. The impact of managerialism on professional bureaucracies is examined using the neo-Weberian framework of hyper-rationality, an ideal type derived from a combination of four forms of rationality identified in Weber's work: practical, formal, substantive and theoretical rationality. Applied to the social organisation of health-care work, this paper critically examines the utility of the hyper-rationality ideal type, noting its limitations and the insights it provides in conceptualising the impact of managerialism on professional (public) bureaucracies.