Recent surveys in Ngamiland, Botswana, indicate increasing prevalence of Schistosoma mansoni infections. With the introduction of a schistosomiasis control programme, 354 of 373 schoolchildren were examined quantitatively for eggs of S. mansoni, and 317 were examined clinically for hepato- and splenomegaly. 80.5% of the children examined parasitologically were found infected. Among these the arithmetric mean egg output was 744.7 and the geometric mean 307.3 eggs per gram of faeces (epg), 46.0% were excreting more than 400 epg. 23 children were found to have an enlarged liver, whereas none was found with enlarged spleen. 21 of these had schistosomiasis. The prevalence of hepatomegaly was highest among those excreting above 1600 epg. Also the mean size of the enlarged livers increased with intensity of infection.