Background: Immunologic and inflammatory responses of cardiopulmonary bypass(CPB) influence postoperative mortality and morbidity with multiple organ injury. It has been reported that ischemia/reperfusion induced-myocardial injury during CPB is causative of release of inflammatory cytokines such as interleukin-6(IL-6) and tumor necrosis factor-$alpha$ (TNF-$alpha$). The purpose of this study was to detect the time course of the activated cytokine and troponin-T(TnT), and to examine the correlation between such parameters during CPB. Material and Method: The serial samples were collected from arterial blood via radial arterial catheter in 23 patients who are underwent open heart surgery (OHS) with CPB, the IL-6, TNF-$alpha$ and TnT were checked. Result: circled1 IL-6, TNF$alpha$- and TnT concentration increased significantly during CPB with a peaking level of CPB-off (p 0.05). circled2 IL-6 had highly positive correlation with aortic cross clamping time and total bypass time(r=0.80, 0.78; p 0.05, respectively). circled3 There was no correlation among IL-6, TNF-$alpha$ and TnT. Conclusion: In conclusion, these data showed that elevated production of serum IL-6 during CPB was attributable to ischemia/reperfusion induced-myocardial damage. IL-6 will become a new and sensitive biological marker in assessment of myocardial damage during OHS with CPB. However, further studies will be needed to apply IL-6 in more patient population.