BACKGROUND: Cardiopulmonary bypass provokes a vigorous inflammatory response and gut mucosal ischemia, which have important implications on the morbidity of cardiac surgery. The purpose of this study was to investigate the effect of a leukocyte-depleted priming solution on inflammatory response and tissue perfusion during cardiopulmonary bypass (CPB). METHODS: Twenty mongrel dogs received hypothermic (28degress C) partial CPB for 2 hours with blood-containing (C group, n = 10), or leukocyte-filtered (LD group, n = 10) priming solution. Gastric intramucosal PCO2 (PrCO2), pHi (pHi), IL-8, blood gas analysis and hemodynamic parameters were measured; 1) before CPB, 2) 1 hour into CPB, 2) 2 hours into CPB, 3) 2 hours after CPB, and 4) 4 hours after CPB. The ratio of wet to dry weight of lungs was measured. Statistical verification was performed using repeated measures ANOVA and unpaired t-test. RESULTS: All baseline data were comparable in the groups. Gastric intramucosal PCO2 increased and pHi decreased during the experiment ithout significant difference between the groups. IL-8 increased in both groups, however, it was lower in the LD group. The difference between PaCO2 and end-tidal CO2 increased during CPB in both groups, and was lower in the LD group. The ratio of wet to dry lung weight was significantly lower in the LD group. CONCLUSIONS: We conclude that the leukocyte depletion from the priming solution attenuates the inflammatory reaction and pulmonary edema induced by hypothermic CPB. The impairment of splanchnic perfusion during CPB may not be related to leukocyte in priming solution.