A total of 52,033 sandflies, comprising 33 species, was collected in tree buttresses in Panama. Of the 18,025 females collected, 1,592 (8.8%) engorged phlebotomines of 18 species contained sufficient blood for identification of their vertebrate hosts by the microcapillary precipitin method. Lutzomyia ylephiletor and Lu. trapidoi, vectors of Leishmania braziliensis, had fed predominantly on sloths (47.0% and 65.1%, respectively). Lutzomyia shannoni, a common non-anthropophilic sandfly in tree buttresses also fed most frequently on sloths (28.0%) and probably also contributes to the Leishmania transmission cycle among the edentates. Two-toed sloths (Choloepus hoffmanni), the principal reservoir of L. braziliensis in Panama, cohabit the same arboreal bioptope with these sandfly species. Leishmania braziliensis was isolated in culture from 14 of 68 (20.6%) C. hoffmanni captured in the study sites during the period of this investigation. The data illustrate that the buttresses of large trees in Panama represent potential pathobiocenose bioptopes of L. braziliensis. Other sandfly species tested for host-feeding sources included: Lu. trinidadensis, which fed preferentially on reptiles; Lu. triramula, Lu. ovallesi, and Lu. camposi fed most frequently on armadillos. The hosts of 11 additional sandfly species were identified; however, the numbers recorded were too small to discern distinct feeding patterns among these phlebotomines.