Furthermore, capping was inhibited when 0.2 M a-D-manoside was present in the system. When 250 ,/g/ml of FITC-Con A was incubated with the amastigotes at 4 C for 60 min, the amastigotes were agglutinated and showed a diffuse surface fluorescence. This pattern did not change when the temperature was raised to 37 C, indicating that the mobility of surface receptors for Con A was inhibited by cell-to-cell cross-bridging or intercellular agglutination. When FITC-WGA, also pretested as described by Katzin et al. (loc. cit.), was used with the amastigotes, they remained unstained, confirming that binding sites for this lectin were not present on the surface of this stage of the parasite. However, receptors for WGA have been demonstrated on T. cruzi epimastigotes by agglutination and fluorescence, and in trypomastigotes by fluorescence urthermore, capping was inhibited when 0.2 only (Katzin et al., loc. cit.). In view of these results we conclude that quantitative and topographical differences, at least with respect to residues of N-acetylglucosamine, occur in the surface membrane of the three different developmental stages of T. cruzi. This work was supported in part by the UNDP/World Bank/World Health Organization Special Programme for Research and Training in Tropical Diseases, from Conselho Nacional de Desenvolvimento Cientifico e Tecnolo6gico (CNPq), from Financiadora de Estudos e Projetos-FINEP-(Grant 527/CT), Brazil, and from Secretaria de Ciencia e Tecnologia (SECYT), Argentina. We are grateful to Mark Crane and Gabriel Schmunis for editorial assistance. Address all correspondence to W. Leon. l (Katzin et al., lo . cit.). In view of these