Sporocysts from tiger snakes (Notechis ater) produced thick-walled sarcocysts in laboratory rats (Rattus norvegicus). Ultrastructurally these organisms were identical with sarcocysts found in native rats, but were different from Sarcocystis singaporensis. Sarocystis murinotechis sp.n. is proposed for this parasite of rodents and tiger snakes. When naturally-infected rats were fed to kittens (Felis domestica), quolls (dasyurus viverrinus) and a masked owl (Tyto novaehollandiae) no sporocysts were detected in the faeces of these animals. Also, sporocysts from owls (T. novaehollandiae and Ninox novaeseelandiae) were not infective for rats (R. norvegicus).