A skin-inhabiting species of Leishmania found in Panama in the tropical porcupine, Coendou rothschildi, is considered new and described as Leishmania hertigi sp. n. L. hertigi is differentiated from other species of Leishmania found in mammals mainly by the nature and course of the infection in its natural host. It is apparently harmless to its host, in which it produces a long-lasting infection, showing a well-established host-parasite relationship. There is a complete absence of any gross skin alteration due to the infection, although the parasite frequently is found in skin over the whole body. L. hertigi seems to be host-specific. In the search for reservoir hosts of human cutaneous leishmaniasis in Panama a new approach was initiated at the Gorgas Memorial Laboratory in March 1965. Starting from the hypothesis that natural leishmanial infections among animals might occur with no gross skin alterations, wild-caught mammals were investigated using skin smears and the recently described biopsy-skin-culture technique (Herrer et al., 1966). The latter technique greatly simplified the detection of parasites in the skin and proved to be very useful in these studies. Early in the investigation, a tropical porcupine, Coendou rothschildi Thomas, was found lightly infected. Subsequent studies showed a high prevalence rate. Morphological and other studies indicate that this is a new species which is described in this paper and named Leishmania hertigi. MATERIALS AND METHODS Porcupines (C. rothschildi) were obtained alive from different localities throughout the central part of the Republic of Panama. Skin from several parts of the body was cultured by the biopsy-skin-culture technique. Skin cultures were made periodically from porcupines maintained in captivity to study the course of the infection. Cultures were also made from skin, liver, and spleen at autopsy. Skin smears were prepared only in certain cases, and skin samples were preserved for sections from animals with positive skin smears. Senekjie's culture medium was used throughout this study, and all cultures were incubated at 19 to 22 C. The parasite could be maintained for about Received for publication 8 September 1970. * The work reported here was supported in part by the research grant AI-01251 from the NIAID, NIH, USPHS. a month before transfer to a new culture. Promastigote (leptomonad) flagellates used for the morphological description were from 2 strains maintained for several months after isolation and were taken from the culture slant 6 to 8 days after a transfer. Drawings were made with the aid of a camera lucida and 80 flagellates were measured for the description. Leishmania hertigi sp. n. (Figs. 1-18) Morphological description (all measurements in microns)