Peripheral blood leukocytes interact with the endothelial lining of the cardiovascular system in a wide variety of physiologic and pathophysiologic situations. In various types of acute and chronic inflammatory reactions, for example, polymorphonuclear leukocytes (neutrophils, basophils, eosinophils) and mononuclear leukocytes (monocytes, lymphocytes) adhere to and then migrate across the locally activated endothelial lining to form an inflammatory exudate. This process involves the ligand-receptor pairing of a series of adhesion molecule expressed by both circulating leukocytes and the endothelial cell (1). The sequential and coordinated interaction of these leukocyte-endothelial adhesion molecules, in conjunction with the localized generation of leukocyte-selective chemoattractant cytokines, confers a cellular selectivity to these reactions (1,2).