Objective To investigate the effects of ulinastatin ( UTI) on renal function after cardiopulmonary bypass (CPB) .Methods Twenty-four NYHA functional capacity class Ⅱ - Ⅲ patients (15 male, 9 female) aged 24-52 yr, weighing 41-75 kg undergoing valve replacement with CPB were randomly divided into two groups :group ulinastatin (group U, n = 12) and group control (group C, n = 12) . Anesthesia was induced with midazolam 0.1 mg ? kg-1 , fentanyl 10 55% ? kg-1 and vecuronium 0.15 mg ? kg-1 and maintained with intermittent iv boluses of fentanyl, midazolam and vecuronium supplemented with isoflurane inhalation. In group U UTI 300 000 U was added to the priming solution and 300 000U/d was infused iv on the first three days after operation. In group C normal saline was given iv instead of UTI. Blood samples were taken and urine was collected before operation (T0), on the 1st (T,), 3rd (T3), 5th (T5) and 7th day (T7) after operation for determination of serum urea nitrogen (BUN), creatinine (Cr), ? 2-microglobulin (? 2-MG) and urinary ?2-MG, RBP and NAG. Results (1) There were no significant differences between the two groups with respect to age, sex, body weight, CPB time and aortic cross-clamping time. (2) BUN, Cr and serum ? 2-MG levels increased significantly after operation at T1 and/or T3 as compared with the baseline values (T0) in group C and were significantly higher than those in group U at the corresponding time points ( P