Proteinuria was studied in 128 children aged 6 to 18 years with Schistosoma haematobium infection in the People's Republic of Congo. Urinary protein concentration in spontaneously voided midday urine of patients with > 100 ova/10 ml was significantly higher than in 24-hr urine specimens. Median daily urinary protein loss in patients with moderate intensity of infection (100–350 ova/10 ml) was 300 mg and 584 mg/1.73 m2 body surface in heavily infected patients (> 350 ova/10 ml). A significant correlation existed between egg excretion at noon and protein concentration in spontaneous urine samples as well as daily urinary protein loss (r = 0.76 and r = 0.68, respectively). Heavily infected patients had a daily protein loss of up to 3.3 g/1.73 m2, total serum protein and albumin concentration, however, were within normal limits. This may indicate adaptive mechanisms in patients with urinary schistosomiasis and high proteinuria which maintain a balanced serum protein concentration.