BACKGROUND: Since hydroxyethyl starch has colloidal properties closely approximating those of human albumin, it is considered to be a good plasma volume expander. Pentastarch is a hydroxyethyl starch similar to hetastarch, but with lower average molecular weight and molar substitution ratio. These characteristics result in enhanced enzymatic hydrolysis, faster renal elimination and less effect on coagulation. This study was designed to evaluate the safety and clinical efficacy of 10% pentastarch in priming fluid for cardiopulmonary bypass compared with that of 5% albumin. METHODS: Thirty- two adult patients undergoing elective cardiac surgery were randomized into two groups. Sixteen patients received 500 ml of 10% pentastarch and sixteen patients received 100 ml of 20% albumin in a bloodless priming solution for cardiopulmonary bypass. The fluid balance, coagulopathy and organ functions(cardiac, pulmonary and renal) were evaluated at several time intervals. RESULTS: There were no differences between the two groups in operation and bypass time, chest tube drainage and blood usage. The measured prothrombin time, partial thromboplastin time and platelet count of pentastarch group were not significantly different from those of the albumin group at each time interval(p<0.05). We did not find any differences of statistical significance in hemodynamic data, serum osmolarity, pulmonary shunt and BUN between the two groups(p<0.05). CONCLUSIONS: Our study suggests that 10% pentastarch can be used safely and effectively as cardiopulmonary bypass prime in cardiac surgery.