Heterophile-antibody titers were determined in sera from apparently healthy individuals and from patients infected with Schistosoma mansoni. The conglutination technique demonstrated ag- glutinating titers equal to or higher than 1:40 in 100% of the schistosome patients, in 80% of the pa- tients with helminthiases other than schistosomiasis, and in 62% of the apparently healthy individuals. In the same groups, the percentages obtained by the conventional technique were 48, 26, and 4%, re- spectively. The higher sensitivity of the conglutination technique for detecting heterophile antibodies, as compared with the conventional one, was clearly shown. Considering the specificity and reliability of many serological tests available for the diagnosis of schistosomiasis, titration of heterophile antibodies has no practical value for this purpose.