Protozoan parasites of the genus Sarcocystis have been recognised for many years as intramuscular cysts of numerous vertebrates. It is only comparatively recently that the two-host nature of the life cycle has been recognised and that the intramuscular cysts are a stage in the developmental cycle of coccidian parasites of flesh eating mammals (Fayer 1974, Fayer and Johnson 1973, 1974, Rommel and others 1972, Dubey 1976). Carnivores ingest the intramuscular cysts from herbivores and presumably from other animals too and eventually shed sporulated tetrazoic sporocysts in their faeces. The cystic stages which occur in the flesh of herbivores are probably non-pathogenic but the earlier stages in which schizonts develop in vascular endothelium may be severely pathogenic. Sarcocystis cruzi, S ovicanis and S porcifelis are known to be severely pathogenic in cattle, sheep and pigs respectively (Dubey 1976). Observations on the prevalence of Sarcocystis spp in the faeces of working farm dogs, greyhounds and foxes (Vulpes vulpes) are recorded.