Intracellular invasion is an important aspect of Carrión's disease caused by Bartonella bacilliformis. Both the hematic and tissue phases of the disease involve the initial attachment of the organism to erythrocytes and endothelial cells, respectively. Using two different approaches, preliminary evidence is provided that B. bacilliformis interacts with multiple surface-exposed proteins on human erythrocytes. Utilizing Western blot analysis, it was demonstrated that the organism binds several biotinylated erythrocyte proteins with approximate molecular masses of 230, 210, 100, 83 and 44 kDa. There was enhanced Bartonella binding to the 44 kDa protein and binding to a 25 kDa protein following exposure of intact red cells to trypsin. Moreover, there was a complete abrogation of binding to these proteins following exposure of erythrocytes to sodium metaperiodate oxidation, indicating the significance of carbohydrate moieties in the interactions of Bartonella with the erythrocyte. In a second approach, similar binding proteins or putative receptors were identified when Bartonella was co-incubated with isolated membrane proteins from red cell ghosts. A comparison of the molecular weights of these putative receptors with known erythrocyte proteins and their immunoreactivity to specific antisera suggested that the 230 and 210 kDa proteins are the alpha and beta subunits of spectrin; the 100 and 83 kDa proteins are band 3 protein and glycophorin A, respectively; and the 44 and 25 kDa proteins are the respective dimeric and monomeric forms of glycophorin B. Consistent with this notion was the binding of Bartonella to purified preparations of alpha and beta spectrin and glycophorin A/B.