The blood meals of 2,569 phlebotomine sandflies from areas endemic for cutaneous leishmaniasis in the central Amazon of Brazil were tested by the microcapillary precipitin method to determine their vertebrate hosts. The two-toed sloth, Choloepus didactylus, was the predominant host of two incriminated vectors of Leishmania braziliensis guyanensis in the region, Lutzomyia umbratilis and Lu. anduzei (64.0% and 63.6%, respectively). The Lu. “shannoni” group, a complex of several species in which females are indistinguishable, also fed predominantly on sloths (73.0%). Species comprising the Lu. “shannoni” group have not been implicated as vectors of leishmaniasis; however, their feeding patterns in the study area illustrate their potential involvement in the transmission of the parasites to two-toed sloths, which are the principal reservoir hosts of L. braziliensis in Panama. Rodents, and particularly porcupines, were the second most frequently fed-on mammal by Lu. umbratilis (11.6%) and the Lu. “shannoni” group (8.5%).