Between June 1997 and May 1998, 47 pit vipers (Bothrops jararaca) (Group A) were euthanased when they were brought to the Instituto Butantan by farmers, and examined postmortem; during the same period, 91 snakes of the same species (group B) were examined after they had died in an outdoor serpentarium. The majority of the parasites encountered were nematodes; lungworms, Rhabdias vellardi, and the intestinal hookworm Kalicephalus inermis were the most common. Some of the snakes in group A were heavily infested, but their lesions were mild, whereas in group B the parasites were generally accompanied by severe lesions. The parasites with a direct life cycle were more common than those with obligatory intermediate hosts, and the snakes were more commonly infected during the hotter and more humid seasons.