In a prospective study of renal involvement in 100 consecutively hospitalized patients with hepatosplenic schistosomiasis mansoni, 15 exhibited persistent proteinuria of varying degree, which in 6 instances was accompanied by hypertension. Nine patients had the nephrotic syndrome. The most common glomerular lesion in this group was membrano-proliferative glomerulonephritis. Surgical biospy obtained during splenectomy in 15 patients without clinical evidence of renal involvement showed glomerular lesions in 6 instances. Focal proliferative glomerulonephritis was the most common lesion in this group. The detection of silent glomerular lesions in patients with Schistosoma mansoni infection suggests that the glomerular alterations may precede clinical manifestations of renal disease.