Abstract.Sphaerospora angulataFujita, 1912, has been identified as a frequent renal parasite of cultured carp populations in Hungary. Its prevalence ranged from 10 to 50% in the pond farms surveyed. The youngest carp infected were 21/2–3 months old. Infections were not common in one‐summer fish and tended to become less frequent with increasing age of the host.The developing stages ofS. angulataare found in the contorted tubules of the trunk‐kidney but never invade the parenchymal tissue of the trunk or head‐kidneys. The pansporoblasts developing in the wide proximal segment of the renal tubules, and the spores arising from the pansporoblasts are typically coelozoic parasites, for they apparently do not damage the tubular lining epithelium, nor its brush border. The main adverse effect ofS. angulatais probably depression of resistance owing partly to deprivation of the host of nutrients secreted by the glomeruli and partly to mechanical obstruction of the distal tubular s