The thee members of the selectin family of adhesion receptors were discovered in the 1980's by independent groups using new and powerful monoclonal antibody techniques: the first antibody bound a surface molecule of leukocytes (L-selectin) and specifically prevented homing of lymphocytes into lymph nodes (1); the second set of antibodies recognized an antigen (P-selectin) present on platelets upon activation (2, 3); and finally, a third brpe of antibody bound a cytokine-induced molecule (E-selectin) on endothelial cells and inhibited adhesion of neuEophils to cytokine-stimulated endothelial cells (4). Shortly thereafter, simultaneous cloning revealed that these genes belonged to the same family and suggested a similar function. The selectin receptors are formed of a functional c-t1pe lectin domain, a single EGF domain which may participate in binding activity and various numbers of repeats homologous to complement binding sequences.