Carbohydrates containing terminal nonreducting D N-acetylgalactosamin or D N-acetylglucosamin were identified at the cell surface of Trypanosoma cruzi by an indirect immunofluorescence test using the lectin of the sponge Aaptos papillata. With the method described in this study T. cruzi and T. cruzi-like strains are easy to distinguish from T. rangeli, but not from T. conorhini. The immunofluorescence test presented here may be very helpful for certain diagnostic problems.