Leishmania promastigotes and axenic amastigotes possess a haemagglutination activity (HA). Leishmania attachment to human macrophages was studied after a 30 min incubation in the presence of 10 mM carbohydrates at 37 degrees C. Galactosamine, sialic acid, heparin, mannose, and NAc-mannosamine impaired the attachment of promastigotes and amastigotes to monocyte-derived macrophages and the myelomonocytic cell line THP 1 whereas other carbohydrates had no effect. Preincubation experiments showed that mannose inhibits the macrophage receptor, whereas galactosamine acts on promastigotes. Moreover, the HA is considerably decreased after incubation with macrophages. Our results suggest that promastigotes of different Leishmania species and axenic amastigotes possess a lectin-like receptor with similar specificity, which is in some way involved in the attachment to vertebrate host cells.