This article draws on ethnographic analysis of Christianity in a Papua New Guinean hospital in order to develop a theory of belief as ‘relational action’. It argues that patients' engagements with Christianity in the hospital derive from a concern with medical efficacy rather than a search for meaning. Patients experience the hospital as a space of stasis in which they are unable to establish relationships effectively with either kin or doctors. Through relationships with God, patients hope to become active Christian agents and yield positive material effects on their bodies. There is a growing anthropological consensus that propositional theories of belief are inadequate to describe Christian and non-Christian religious practice. However, there is still a tendency to contextualize belief within wider cultural wholes. This article argues that patients' practice of belief as ‘relational action’ should be interpreted not as an attempt to construct moral and cosmological order in the face of change, but as an attempt to realize themselves as new kinds of social agents in the face of social failure.