Diptera that breed in undisturbed cattle droppings in pastures present great diversity and abundance, and several species are of veterinary importance and may cause economic losses. To survey the diversity, abundance and seasonality of Diptera associated to this microhabitat, 83 samples of 10 dung pats each were taken front April 1992 to April 1994 in the vicinity of Sao Carlos, State of Sao Paulo, Southeastern Brazil. A total of 46.135 Diptera belonging to 20 families and at least 51 species were found to breed in the pats. The most abundant and diverse families were Sepsidae, Muscidae, Sarcophagidae and Sphacroceridae. In general, the abundance was higher from October to March, the warm and wet months. The importance of some Diptera, both as horn fly enemies and as cattle dung decaying agents, is discussed.9713741