Intestinal ischemia-reperfusion (IIR) is a complex phenomenon causing local and remote tissue destruction, and even multiple-organ failure. To examine the hypothesis that IIR affects renal function, 21-day-old male Sprague-Dawley rats underwent 45 min superior mesenteric artery occlusion and control rats were subjected to a sham laparotomy. After 2 and 24 h and 1 week of reperfusion, blood was sampled for urea and the kidneys were harvested for lipid peroxidation and histologic examination. Malondialdehyde (MDA) levels as an indicator of lipid peroxidation were significantly increased in renal tissue after 2 h of reperfusion, and this finding was in accordance with serum urea levels (SU) and endothelial injury. However, at 24 h of reperfusion MDA and SU had returned to normal. These data were supported by electron-microscopic studies suggesting reversibility of the changes. It is concluded that IIR leads to renal injury and that free radicals may be responsible for this injury.