Abstract: Objective To investigate the effect of modified ultrafiltration on attenuating the inflammatory reaction and endothelial cell activation or damage after cardiopulmonary bypass (CPB). Methods Forty patients undergoing cardiac operation with CPB were randomly divided into two groups. Ult rafiltration group ( n = 20) : patients underwent modified ultrafiltration after CPB; control group ( n = 20 ) : without ultrafiltration. Plasma concentrations of soluble intercellular adhesion molecules-1 ( s ICAM -1) and tumor necrosis factor-α (TNF-α) were determined with enzyme linked immunosorbent assay and radioimmunity pre-operat ively (baseline) , at the end of CPB, 4h and 24h post-operatively in both groups. Results The concentrations of sICAM -1 in the cont rol group at 4h and 24h po st-operatively were higher than those pre-operatively (P lt; 0. 01). The concentrations sICAM -1 in the ultrafiltrat ion group in pre-operatively and at the end of CPB were not significantly different from that of the control group, but they were lower at 4h and 24h post-operatively (269. 6±33. 8Lg/L vs. 409. 6±37. 3Lg/L , 245. 9±32. 2Lg/L vs. 379. 3±35. 7Lg/L ; P lt; 0. 01). In the ultrafiltration group, the concentration of TN F-α at the end of CPB and 4h post-operatively were higher than that pre-operatively (P lt; 0. 01). The concent rations of TNF-α in the ultrafiltration group at 24h post-operatively recoved to the pre-operative level (0. 177±0. 024Lg/L vs. 0. 172±0. 030Lg/L ; P gt;0.05). In the control group, the concentration of TN F-α was higher at the end of CPB than that pre-operatively (P lt;0.01) , and decreased slightly at 4h and 24h post-operatively, but remained higher than those pre-operat ively (0. 264±0.045Lg/L vs. 0.174±0.033Lg/L , 0.218±0.028Lg/L vs. 0.174±0. 033Lg/L ; P lt; 0. 05). Conclus ion CPB is known to induce inflammatory reaction and endothelial cell activation or damage. Modified ultrafiltration appears to attenuate these adverse reactions and is beneficial to postoperative convalescence.