A circulating antigen, a negatively charged polysaccharide from the trematode Schistosoma mansoni, was noncovalently bound to the surface of poly(L-lysine)-coated wells in polystyrene trays, which were then used in a micro-enzyme-linked immunosorbent assay (ELISA) test. The method provides an immunodiagnostic test for schistosomiasis of exceptional sensitivity with a high degree of specificity. Comparison of Bell egg counts and ELISA titers revealed a good correlation (r congruent to 0.80) in young individuals with low to moderate worm burdens, but this relationship was less marked in older individuals or those with high egg counts.