The applicability of a Schistosoma mansoni polysaccharide antigen, circulating cathodic antigen (CCA), for the detection of antibodies in S. mansoni infection was tested in the enzyme-linked immunosorbent assay (ELISA). Antibodies against this secretory antigen were detected in hamster infections after three weeks, while in infected humans anti-CCA antibodies could be demonstrated eight weeks after infection. Antibodies could be demonstrated both in recent and chronic infections in man, but more false-negative results were observed in chronic infections. The antibody response was composed of both IgM and IgG antibodies.