This paper is based on long-term ethnographic fieldwork among the Lelet of New Ireland Province, Papua New Guinea. It draws on qualitative interviews with Pentecostal Christians intended to examine their understanding of Christianity and how this relates to their cultural practices - in this case, how their Pentecostalism affects their therapeutic beliefs and practices. The frequent observation that therapeutic repertoires are becoming less discrete is substantiated by the Lelet case, for in their search for therapy, the Lelet often cross the borders of different repertoires, seeing no contradiction, for example, between combining a vernacular therapy with biomedicine. With the advent of Pentecostalism, the issue has become far more complex. The Lelet therapeutic culture remains pluralist, but the research shows that Lelet Pentecostals are increasingly viewing their own Christian-based forms of healing as in competition with other therapies, especially vernacular therapies. This competitive outlook has brought a demonization of vernacular therapies, which are labelled 'satanic' and their use discouraged. In fact, Pentecostalism is refashioning the realm of therapy: rather than border crossing and mixing of therapeutic repertoires, the situation is increasingly dominated by notions of mutual exclusivity. In order to comprehend the full complexity of medical pluralism, it is now necessary not only to examine how the borders of the different therapeutic repertoires are blurred, destabilized or reconfigured but also how they may be demarcated and policed. In other words, we argue that medical pluralism is being eroded by its interaction with Pentecostalism.