A survey for schistosomiasis in a village in the Gezira area of the Sudan in 1973 showed that there has probably been a great increase in the incidence of S. mansoni infection in the last 25 years. Severe morbidity was uncommon in this sample but overt infection was associated with the symptoms of bloody diarrhoea, tiredness, and possibly abdominal pain, and with a reduced level of haemoglobin. Hepatosplenomegaly was common and schistosomiasis is considered to have contributed to this, although hyperendemic malaria must also have been important in its causation.