A prevalence, intensity and morbidity study was carried out at a primary school amongst 681 pupils aged 6-15 years. A comprehensive medical examination including urinalysis was carried out. Attendance at school and average grades scored during the preceding schoolyear were used as crude indiced of performance. The overall prevalence rate was 24%. The mean egg count was 435 ova/10 ml urine in infected children. Haematuria was observed in 65% of infected children with the greatest intensity in patients with the highest egg count. Both the haematocrit (PCV) and haemoglobin concentrations bore no relationship to the intensity of infection; whilst there was a direct relationship between the level of proteinuria and the number of ova excreted. Proteinuria of more than 100 mg/100 ml was found in 54% of subjects and in 23% of these it was 300 mg/100 ml. Anthropometric measurements were not related to intensity of infection nor were attendance and the average scored during the preceding schoolyear. It is concluded that probably only minimal morbidity is associated with S. haematobium infection in this area; this may be explained by the relatively low intensity of infection including acquired immunity and the seasonal pattern of transmission.