Katayama fever or acute schistosomiasis probably occurs more commonly than is recorded. Interviews with a 3-man scuba diving team who had had contact with a large dam in an endemic area of the eastern Transvaal Lowveld at the same time and contact area on the same day during late summer of 1986 are discussed. Two, who had not previously been exposed to infected water, presented with Katayama fever, due to Schistosoma mansoni infection, 21 days after contact and it took 30-36 months for them to recover fully after several treatments. The third patient, a keen water-sportsman and resident in the endemic area for a period of 10 years, presented with a mild infection, probably due to acquired immunity initiated during previous contacts with infected water; he took about a year to recover. The pathogenesis, clinical features, diagnosis and treatment of the 3 cases are described in the light of recent observations made elsewhere on Katayama fever cases and the effects of chemotherapy on the course of illness. The necessity of obtaining basic information on the travel and water-contact activities of patients in order to make a diagnosis is emphasised.