A serological survey in the Gezira area of the Sudan confirmed that malaria and schistosomiasis were highly endemic. Of other parasitic infections amoebiasis was common but Toxoplasma was less than found in a previous survey. Poliomyelitis and measles infection were universal and there was an extremely high incidence of infection with hepatitis B. Of arboviruses infection with flaviviruses was frequent and more than with alphaviruses.