This study was performed to evaluate the effect of prostaglandin E1 (PGE1) on renal function after cardiac surgery in patients undergoing cardiopulmonary bypass (CPB). Haemodynamic and renal functional response to low dose PGE1 (0.02 microgram kg-1 min-1) (group A) or saline (group B) infusion via peripheral vein during CPB was evaluated in 20 patients who underwent cardiac surgery. The perfusion pressure was maintained at about 60 mmHg during CPB in both groups. Urine beta 2-microglobulin (UBMG) (P < 0.01), and urine N-acetyl-beta-D-glucosaminidase (NAG) (P < 0.05) demonstrated significantly high values after CPB in both groups compared with the presurgical value. Free water clearance (CH2O) decreased significantly at the first postoperative day compared with the pre-surgical value in both groups (P < 0.01). Statistical analysis of NAG, UBMG and CH2O demonstrated significant differences between both groups, in CH2O values at the third (P < 0.05) and fifth days (P < 0.05) after surgery, in NAG values at the fifty (P < 0.01) and seventh days (P < 0.01), and in UBMG values at the first (P < 0.05) and third (P < 0.05) postoperative day, respectively. Cardiac output (co) did not change in either group throughout this study. Pulmonary capillary wedge pressure (PCWP) in group A decreased significantly at 30 and 60 min after CPB, but in group B did not change throughout the study. Cardiac index (CI) decreased significantly at 60 min after CPB in group A (P < 0.05) and at 30 min in group B (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)