Forty-six samples of nematodes recovered from Brazilian specimens of Crotalus durissus Linnaeus, 1758, commonly named rattlesnake were studied. Snakes either died in captivity, under which they were kept for production of serum, or were found dead in nature. Other samples of nematodes from this host and preserved} in the Helminthological Collection of the Oswaldo Cruz Institute (CHIOC) were also analyzed. The most prevalent species were those of the genus Ophidascaris Baylis, 1920: O. arndti Sprehn, 1929, O. durissus Panizzutti, Santos, Vicente, Muniz-Pereira & Pinto, 2003, O. sicki Freitas, 1951, O. tuberculatum Siqueira, Panizzutti, Muniz-Pereira & Pinto, 2005 and Ophidascaris sp., followed by specimens allocated in Hexametra Travassos, 1920: H. boddaertii (Baird, 1860) Kreis, 1944, and Kalicephalus Molin, 1861: K. inermis macrovulvus Caballero, 1954, Kalicephalus sp. Also, spe...

Results of fecal examinations have been compared with those obtained during necropsies of snakes infected with helminths. Stool samples from specimens of Bothrops jararaca and B. alternatus were investigated and three animals were positive for eggs during coprological screenings: one case representing authochtonous snake parasites, other related to species accidentally introduced together with naturally infected mice snakes fed on, and another with the association of both. Necropsies of those same specimens, showed the presence of the nematodes Ophidascaris travassosi Vaz, 1938, Kalicephalus costatus (Rudolphi, 1819), K. inermis Molin, 1861, Kalicephalus sp. and Acanthorhabdias acanthorhabdias Pereira, 1927. Bothrops jararaca is a new host record for O. travassosi and Bothrops alternatus for A. acanthorhabdias; the gross pathological lesions induced by the nematodes are reported.