Objective To investigate the effects of ulinastatin on cerebral injury during cardiac valve replacement and the possible mechanisms involved. Methods Twenty-four NYHA Ⅱ or Ⅲ patients of both sexes (13 male, 11 female) aged 23-45 yr undergoing cardiac valve replacement with hypothermic cardiopulmonary bypass (CPB) were randomly divided into two groups: control group (group C, n = 12) and ulinastatin group (group U, n = 12) . In group U ulinastatin 12 000 U?kg-1 was given i.v. after induction of anesthesia, 6 000 U? kg-1 was added to the priming solution and another 6 000 U?kg-1 was given at 5 min before aortic unclamping. In group C normal saline was given instead of ulinastatin. Internal jugular vein was cannulated and the catheter was advanced in a cephalad direction till jugular bulb. Blood samples were taken from jugular bulb after induction of anesthesia(T1) , when rewarming to 36℃(T2), 30 min (T3 ) and 6 h (T4 ) after discontinuation of CPB for determination of plasma S100? protein, neuron specific evolase (NSE) , MDA concentrations and SOD activity. Plasma TNF-?, IL-6, IL-8 and IL-10 levels were also determined at T1, T3 and T4.Results Plasma levels of S100? protein, NSE and MDA were significantly increased during and after CPB (T2-4) compared to the baseline values before CPB (T1), but were significantly lower in group U than in group C (P