Endothelial cell activation and the cell surface expression of adhesion molecules are considered to be crucial steps in the systemic inflammatory response to cardiopulmonary bypass. Endothelial cell adhesion molecules mediate the process of leukocyte adhesion to the endothelium and their subsequent transmigration and degranulation in the subendothelial tissues. The levels of soluble endothelial adhesion molecules in plasma have been used to draw conclusions regarding the cell surface expression of these molecules; the limitations of such studies are discussed. Inhibition of cell adhesion molecules may prevent the inflammatory condition caused by cardiopulmonary bypass and reperfusion injury. Further studies are needed to define the role of endothelial cell adhesion molecules in this inflammatory response.