The purpose of this project is to characterize the polysaccharides isolated from certain species of flagellate protozoa of the parasitic family Trypansomatidae. Our results indicate that these polysaccharides are a constituent of the surface membrane of these organisms. An arabinogalactan has been isolated from Crithidia fasciculta and localized at the cell surface by means of a specific antiserum employed in agglutination and immunocytochemical studies. A carbohydrate containing antigen prepared from culture forms of Trypanosoma cruzi, and present at all stages of the life cycle and in all strains tested, has similarly been localized at the cell surface. Antibodies to this antigen have been detected in the plasma of mice acutely infected with T. cruzi. Present and future work includes: 1) further chemical analysis of these carbohydrates; 2) study of the relationship of these carbohydrates with other components of the cell surface and membrane; and 3) study of the physiological significance of these molecules and their possible role in the infectious process. The mechanism of hexose transport in Leishmania tropica is being studied. In particular a phosphorylating activity which may be involved is studied.