Neutrophil-endothelial adhesion is the initiating event in neutrophil migration to areas of infection or injury. The binding of neutrophils to endothelium depends upon adhesive glycoproteins, of which the CD11/CD18 glycoproteins are the most important. Because of known upregulation of one of these adhesive glycoproteins (CD11b) during cardiopulmonary bypass (CPB) in humans, we evaluated CD11a, CD11b, and CD11c surface expression before, during, and after CPB in humans, with or without pre-CPB administration of a glucocorticoid (methylprednisolone). Fourteen patients were randomized into two groups: Group S received methylprednisolone (1 g intravenously) 5 min prior to CPB; Group N received no steroid. CD11b was significantly upregulated (P < 0.01) during, and 24 h after, CPB in Group N when compared with controls and Group S at similar time intervals, while in Group S no significant changes were found. Since interleukin-1, tumor necrosis factor, and endotoxin are known to upregulate neutrophil CD11b surface expression and are released during CPB in humans, while steroids are known to suppress the release of these cytokines, the authors conclude that the blunting effect by steroids on CD11b surface expression upregulation during and after CPB in humans is attributed to suppressed cytokine release.