A leishmanial parasite was isolated from 11 of 18 porcupines from the general area of Ponta de Pedras, Island of Marajó, Pará State, north Brazil. Two of the infected animals were identified as Coendou prehensilis (Linnaeus), and the other 9 are considered as a hitherto undescribed species of Coendou. The organism is clearly related to L. hertigi Herrer, of the Panamanian porcupine C. rothschildi Thomas, but morphological, serological and biochemical differences necessitate taxonomic distinction. The Brazilian parasite is therefore named Leishmania hertigi deanei nov. subsp., in honour of Dr. Leonidas Deane who first recorded it in porcupines from Piaui, Brazil. Lake L. h. hertigi, L. h. deanei produces no visible pathological effects in its natural host. Scanty amastigotes are scattered, often singly, throughout the skin and in the viscera; usually they can be detected only after the in vitro culture of tissues in "blood-agar medium, in which L. h. deanei grows readily. Attempts to infect hamsters and a guinea-pig with amastigote and promastigote forms were unsuccessful. The sandfly vector of the parasite is unknown.