We report a severe enteric infection of Sarcocystis sp. from a wild-caught bull-snake (Pituophis melanoleucus sayi). The animal was collected in October 1988 by a commercial dealer, imported into the United Kingdom during November 1988 and purchased by the London Zoo, in December 1988. The animal was not fed after capture and was anorexic from the time of purchase to the time of death in January 1989. On necropsy, the animal was emaciated and the mucosa of the proximal intestine was markedly thickened. The lamina propria was packed with oocysts, and enterocytes were parasitized by an organism which closely resembled Sarcocystis roudabushi and Sarcocystis idahoensis, two bisporocystid coccidia described previously from Pituophis melanoleucus. We propose that Sarcocystis idahoensis and Sarcocystis roudabushi are synonymous since both occur in the same host species, both invade the intestinal lamina propria and enterocytes, and sporocyst measurement ranges of both species overlap. This is the first report of death believed to be due to sarcocystosis in a naturally-infected definitive host.