Differentiation of promyelocytic HL-60 cells along the pathway toward granulocytes using dimethyl-sulfoxide (DMSO) led to increased expression of the adhesion molecules CD11b (Mac-1), CD11c (p150,95), and CD35 (CR1). Undifferentiated and differentiated HL-60 cells adhered similarly to Entamoeba histolytica trophozoites, and monoclonal antibodies against adhesion molecules CD11b and CD11c did not inhibit adherence. We therefore suggest that CD11b and CD11c are not involved in the adherence between polymorphonuclear granulocytes and E. histolytica trophozoites.