Two Leishmania donovani glycoconjugate ligands for the internalization receptor on BALB/c peritoneal macrophages [fucose-mannose ligand (FML) and phosphate mannogalactan ligand (PMGL)] were shown to be species-specific in a comparative phagocytosis-inhibition test. Promastigotes of L. donovani Sudan (LD1S), L. infantum, L. d. donovani, L. major (Jericho and Sudan), L. tropica, L. chagasi, L. mexicana venezuelensis, L. m. mexicana, L. m. amazonensis, L. m. pifanoi, L. m. garnhami, L. braziliensis braziliensis, L. m. amazonensis (Josefa), L. enrietti or L. adleri were incubated with macrophages in the presence of 10 micrograms/ml FML and PMGL purified from L. donovani (LD1S). Parasite internalization was determined and compared with that obtained in control experiments. Specific inhibition of phagocytosis ranged from 83% (L. donovani LD1S) to 7% (L. m. amazonensis). We could distinguish groups of Leishmania consistently with their geographic distribution and the clinical aspects of the disease. Analogous experiments with L. m. amazonensis glycoconjugates showed reciprocal results, with inhibition ranging from 76% (L. m. amazonensis) to 8% (L. donovani LD1S). L. chagasi remained separated from the Old World kala-azar agents. Possible phylogenetic implications of these observations are discussed.