Newars, who comprise the indigenous and highly urbanized civilization of the Kathmandu Valley in Nepal, have a complex medical system. This article focuses on one nearly extinct medicine: an oil infused with small bats. These bats are understood by Newars to have become rare due to the changing architecture and rapid suburbanization of the Kathmandu Valley, a process they see as regrettable and forced upon them by regional changes. The history and practice of this medicine is then used as a lens through which to consider a series of parallel tensions: between textual norms and local practices; between the expertise of doctors, priests, astrologers and other male professionals and the expertise of mothers who decide what medicines to use and which professionals to consult; between the situated Newar medical tradition and the regional South Asian tradition that is subsuming it; between local categories and traded goods; and between attempts to describe ethnobiological practices using centralized expertise and the improvised and dispersed way in which many practices are actually achieved and transmitted.