Antisera prepared in rabbits against whole eggs and extracts of cercariae and adults of Schistosoma mansoni were tested with homologous and heterologous antigens by means of the hemagglutination test. Cross-reactions with egg antigens of of 3 schistosome species, cercarial, and adult antigens of S. mansoni were obtained with these sera. With sera of children infected with S. mansoni egg antigen of S. mansoni gave higher titers than cercarial or adult antigens. With sera of 10 adult patients obtained during chronic infection and 1 year after cure, egg antigens and an antigen from adult metabolic products were positive by hemagglutination with 4 sera taken during infection, but not after cure. The hemagglutination test is a sensitive test for the diagnosis of schistosome infections. With the proper antigens it may prove to be a valuable serological method for the evaluation of chemotherapeutic cure. Utilizing saline extracts of various stages as antigens, the hemagglutination test showed no specificity with stage-specific rabbit antisera.