An enzyme-linked immunosorbent assay (ELISA), and radioimmunoassays using antigen bound to plastic tubes or microcrystalline particles, were adapted for the indirect serological measurement of anti-schistosome antibodies. These alkaline phosphatase and 125I-labeled anti-immunoglobulin techniques were found to be highly quantitative and adaptable. Comparison showed them to be considerably more sensitive than the indirect hemagglutination and indirect fluorescent antibody techniques. Using adult S. mansoni freeze-thaw antigen, anti-schistosome antibodies were detected in sera from patients infected with Schistosoma mansoni and S. haematobium. However, results in patients with schistosomiasis haematobium were generally intermediate between those of patients with schistosomiasis mansoni and normal, uninfected controls.