OBJECTIVE The purpose of this study was to investigate the efficacy of carperitide (human atrial natriuretic peptide [h-ANP]) in perioperative management in patients with renal dysfunction, especially its kidney-protecting effects. METHODS The subjects were 18 patients who underwent elective cardiac surgery using cardiopulmonary bypass (CPB) with a preoperative serum creatinine (Cr) level of 1.2 mg/dl or more. The subjects were prospectively assigned to 2 groups: an h-ANP-treated group (Group H, n = 10) and a non-h-ANP-treated group (Group N, n = 8). At the beginning of surgery, h-ANP administration was initiated and continued for 5 days or more. The central dose was 0.02 microg/kg/min. The primary end point included the serum Cr level and creatinine clearance (Ccr). RESULTS In Group H, Cr level significantly decreased after surgery compared to the preoperative level. The Ccr values were significantly higher 2 and 3 days after surgery than the preoperative values. And the intraoperative urine volume significantly increased. In Group H, an increase in urinary N-acetyl-beta-D-glucosaminidase (NAG) level the day after surgery was significantly inhibited in comparison with Group N. CONCLUSIONS The results of this study suggest that in patients with renal dysfunction before cardiac surgery, continuous low-dose h-ANP therapy maintains renal function, preventing its deterioration.