Polyclonal antisera to 80 - 90-kDa and to 50 - 60-kDa polypeptides of tissue-culture trypomastigotes which inhibit the interiorization of trypomastigotes of the Y strain (up to 70%) and of metacyclic trypomastigotes of the CL-14 clone (up to 50%) in cultured mammalian cells, were obtained. Both sera immunoprecipitate surface polypeptides of 90 kDa, 80 kDa, 72 kDa and 58 kDa in trypomastigotes and of 80 kDa, 77 kDa and 74 kDa in metacyclic trypomastigotes. These antigens are glycoproteins with affinity for concanavalin A. The antibodies (IgG class) of the inhibitory sera are mainly directed against carbohydrate epitopes, which were identified as being beta-D-galactofuranosyl units by radioimmunoinhibition assays. The direct involvement of the beta-D-galactofuranosyl unit in the process of parasite infection was verified using the synthetic disaccharide beta-D-galactofuranose (1----3)-alpha-D-mannopyranose which promoted, at 1 mg/ml concentration, 50% inhibition of internalization.