Changes of hemodynamics and chemical mediators before and after aortic clamping were investigated in 12 patients who underwent infrarenal abdominal aortic aneurysmectomy. Patients were divided into two groups; one with an aortic clamping time greater than 1 hour (the long group) and the other with aortic clamping time less than 1 hour (the short group). Cardiac output, mean pulmonary arterial pressure (MPAP), extravascular thermal volume (ETV), polymorphonuclear elastase (PMN-E), α₁ trypsin inhibitor (α₁-TI) superoxide dismutase (SOD), urine N-acetyl-β-D-glucosaminidase (NAG), were measured before and immediately after aortic clamping, immediately after, 1 and 4 hours after aortic declamping. In addition, serum GOT, GPT, creatinine and BUN were measured before and 1, 3 and 7 day after operation. These levels were expressed as ratios of the level before aortic clamping and operation. The MPAP ratio immediately after aortic clamping was 0.83±0.06 in the long group and 0.99±0.08 in the short group. There was statistical significant difference in the MPAP between both groups (p<0.01). In contrast, there was no significant difference in the cardiac output or ETV between the two groups. The PMN-E ratio immediately after aortic declamping was 2.24±0.81 in the long group and 1.19±0.45 in the short group. These ratios increased at 1 and 4 hours after aortic declamping. The PMN-E ratio following aortic clamping in the long group was greater than those in the short group (p<0.05). The SOD at 1 hour after aortic declamping was 0.78±0.13 in the long group and 1.01±0.11 in the short group (p<0.05). The NAG ratio immediately and at 1 hour after aortic declamping was significantly higher in the long group when compared with the short group (p<0.01, 0.1). Serum GOT, GPT, creatinine and BUN ratios showed no change through out this study. There was an increase in protease and a decrease of free radical scavengers in the long group. These findings are commonly known to be linked with organ damage. Through the findings of this study, we suggest that clamping time should be minimized; thus reducing the possible chance of postoperative organ damage.