Hamsters infected with Schistosoma mansoni or S. japonicum develop renal lesions by the 7th week of infection. These are chiefly characterized by mesangial and endothelial glomerular hypercellularity, glomerulosclerosis, tubular dilatation and proteinaceous casts. Fluorescent antibody tests show that host globulin is deposited in the glomeruli, possibly the consequence of immune complexes in antigen excess. Autoradiographic and liquid scintillation counting techniques indicate that increased amounts of deoxyribonucleic acid are retained in the kidneys of infected hamsters as compared to normal controls and may play a role in the pathogenesis of renal disease.