Endothelial leukocyte adhesion molecule-1 (ELAM-1) is an endothelial cell adhesion molecule that allows myeloid cells to attach to the walls of blood vessels adjacent to sites of inflammation. ELAM-1 recognizes the sialyl-Lewis X (sialyl-Le^x) determinant, NeuAcα2-3Galβ1-4(Fucα1-3)GlcNAc-, a granulocyte carbohydrate also found on the surface of some tumor cell lines. Binding of myeloid cells to soluble ELAM-1 is inhibited by a monoclonal antibody recognizing sialyl-Le^x or by proteins bearing sialyl-Le^x, some of which may participate in humoral regulation of myeloid cell adhesion. Stimulated granulocytes also release an inhibitor of ELAM-1 binding that can be selectively adsorbed by monoclonal antibody to sialyl-Le^x.