Antibody (immunoglobulin (Ig) G) to the haemocyanin of the keyhole limpet (KLH) (Megathura crenulata), which shares a well defined carbohydrate epitope with the surface of schistosomula of Schistosoma mansoni, was determined by enzyme-linked immunosorbent assay (ELISA) in the sera of Brazilians with