Because chronic iron overload can cause organ injury in hemochromatosis and because iron participates in injury during renal ischemia-reperfusion, the effect of mild subacute renal iron loading on the susceptibility to ischemic acute renal failure was evaluated. Male Sprague-Dawley rats were injected with iron nitrilotriacetate (1 mg iron/kg BW i.p. daily) for 5 days. Controls were instead injected with nitrilotriacetate. Seventy-two hours later animals were subjected to 40-min renal artery ischemia. Iron loading produced a 28% increase in kidney iron content without any change in baseline renal function (plasma creatinine) or histology. Ischemic renal injury was far more severe in iron-loaded animals. Plasma creatinine 24 and 48 h after ischemia was significantly higher in iron-loaded rats (3.3 and 3.4 vs. 2.2 and 0.8 mg/dL) and GFR was significantly lower in iron-loaded rats (0.30 vs. 0.78 mL/min). In addition, iron-loaded rats showed a dramatically greater extent of damage by histologic evaluation using a semiquantitative scoring method. Therefore, a small increase in renal iron content greatly increased renal injury after an ischemic insult. These findings may be relevant to human renal disease because there is accumulating evidence of renal iron accumulation in a variety of proteinuric and chronic renal diseases.