Fifty consecutive patients who had undergone cardiac operations for various cardiac lesions were investigated prospectively to evaluate the incidence, risk factors and the associated mortality op postoperative hyperbiliruminemia and hepatic dysfunction after cardiopulmonary bypass. Concentrations of serum total bilirubin, alanine aminotransferase (ALT), aspartate aminotransferase, lactate dehydrogenase (LDH) alkaline phosphatese, albumin, globulin were measured before the operation and again on the 1., 2., 7. postoperative days. On the 1. and 2. postoperative days 90% of the patients showed abnormal AST activity on the 7th postoperative dal.ALT levels were significantly higher than the preoperative period (p<0.001). Postoperative hyperbilirubinemia defined as occurence of a serum total bilirubin concentration of more than 3 mg/dl in any measurement during the postoperative hyperbilirubinemia was 38%. The incidence was higher in patients with high preoperative total bilirubin concentrations (p<0.01). Valve surgery, preoperative high right atrial pressure, prolonged cardiopulmonary bypass, preoperative elevated ALT, LDH, alkaline phosphatase are significant risk factor (p<0.001). One patient with late postoperative hyper-bilirubinemia died due to multiple organ failure.