We describe an outbreak of human cryptosporidiosis in 5 veterinary students in contact with experimentally infected calves. All persons experienced symptoms of gastroenteritis, with the main complaint of diarrhoea lasting for 1-13 days. The persons recovered spontaneously; one was hospitalized for 10 days. The diagnosis was based on the demonstration of Cryptosporidium oocysts from stools by the smear method and the formalin-ether concentration method, both combined with the acid-fast staining technique. Both methods gave almost equal results. The role of Cryptosporidium as an occupational risk is discussed.