This paper explores the rise of an audit practice: the national quality registers in Swedish health care. Based on actor-network theory, the study tells the story of an actor-network formed by physicians in the 1970s who mobilized themselves around a common object; to develop the knowledge-base of medical professionals. However, over time more actors became persuaded of the potential of the network and associate themselves with it, resulting in reformed registers. The study shows how the network develops into a macro-actor, a Leviathan in health care, how this macro-actor comes to affect health care practices and how it contributes towards maintaining a new governance regime.