Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine released in response to glucocorticoids, which counter-regulates the effects of glucocorticoids. This study was performed to determine the impact of steroids on the expression of MIF and other pro- and anti-inflammatory cytokines during and after cardiopulmonary bypass (CPB). Twenty adult patients (10 men, 64 ± 8 years old) who underwent elective cardiac surgery by CPB were given either 2000 mg (group-H, n = 10) or 500 mg of methylprednisolone (group-L, n = 10) during CPB. The serum concentrations of MIF, interleukin (IL)-1β, IL-8, IL-10, and tumor necrosis factor-alpha (TNF-α) were measured at eight time points until 36 hours after skin closure. The early postoperative course was uneventful for all patients. There were no significant differences in duration of operation, CPB, or aortic cross-clamping (AXC) between the two groups. MIF and IL-10 levels peaked just after the conclusion of CPB and decreased gradually thereafter. IL-1β, IL-8, and TNF-α were undetectable throughout the study period. There were no significant differences in MIF or IL-10 levels between the two groups. Peak levels of MIF in all patients were significantly correlated with the duration of CPB and AXC, whereas no such correlation was observed for IL-10. MIF or IL-10 levels were significantly elevated during and after CPB, but there were no differences between the two doses of steroid administration. Both steroid doses sufficiently suppressed proinflammatory cytokines. MIF better reflected the invasiveness of the operation than IL-10.