Three Sarcocystis species with snake-rodent life cycles were studied for their host range and host specificity in systematically related intermediate and definitive hosts. While S. singaporensis and S. villivillosi developed only in murids closely related to the genus Rattus, a third Sarcocystis species (natural definitive host: Bitis nasicornis - syn. Isospora dirumpens ?) showed a broad intermediate host range. This species was found to use several Bitis species as definitive hosts. S. singaporensis and S. villivillosi in contrary produced sporocysts only in three Python species and in Aspidites melanocephalus .