The endoparasitic fauna of four mammal species was analyzed: Puma concolor (Linnaeus, 1771) (cougar), Lycalopex gymnocercus (Fischer, 1814) (grey fox), Myocastor coypus (Molina 1782) (coipus) and Tolypeutes matacus (Linnaeus, 1758) (armadillo). These specimens entered the Center for Wildlife Rehabilitation, Environmental Education and Responsible Recreation located in the province of San Juan, Argentina. Out of the four mammal species, three died on the spot. The necropsy of L. gymnocercus, M. coypus and T. matacus was carried out, and it was evidenced the presence of three species of parasitic nematodes: Physaloptera clausa Rudolphi, 1819 (Physalopteridae) in L. gymnocercus; Trichuris myocastoris Enigk, 1933 (Trichuridae) in M. coypus; and adult females of Aspidodera sp. Railliet & Henry, 1912 in T. matacus. Regarding P. concolor, the expulsion of nematodes was orally, determining t...