While the systemic cardiovascular consequences of infrarenal aortic cross-clamping during aortic abdominal surgery are well documented, its repercussions on renal hemodynamics in humans have not been reported. In 12 patients, scheduled for elective aortic surgery, renal clearances, using51Cr EDTA and125I hippuran, were measured before, during, and after infrarenal aortic cross-clamping. A continuous infusion of mannitol 20% at a rate of 100 ml/h was administered throughout the study. Arterial and renal venous blood sampling, obtained at the midpoint of each period, permitted calculation of the extraction fraction of125I hippuran and accurate determination of renal blood flow and its cortical-extracortical distribution. Although cardiac output and systemic vascular resistance did not change significantly between the three study periods, infrarenal aortic cross-clamping decreased125I hippuran clearance by 29 ± 15% (P< 0.05) and renal blood flow by 38 ± 14% (P< 0.001). Simultaneously, an increase of 75 ± 31% in renal vascular resistance (P< 0.05) was observed and the extraction fraction of125I hippuran increased from 0.67 ± 0.05 to 0.74 ± 0.05 (P< 0.01). All of these changes, which indicate global diminution of renal perfusion with a redistribution of renal blood flow toward the cortical compartment, persisted for at least 1 h after release of the aortic clamp. Early signs of renal tubular damage, such as the appearance of lysozyme and ligandine in the urine, however, were never observed. The authors conclude that infrarenal aortic cross-clamping produces profound and sustained alterations in renal hemodynamics and may be harmful in patients with impaired renal function or when surgical occlusion of the aorta is prolonged.