The protective effect of intravenous administration of exogenous prostaglandin E1 on ischemia-induced acute renal failure was investigated in dogs. The parameters studied were renal cortical blood flow, renal function, survival time, and histologic changes. The model was prepared by clamping the renal artery for 1 or 2 hours. Renal cortical blood flow was measured by the hydrogen washout technique. After prostaglandin E1 administration, renal cortical blood flow increased significantly and renal function was maintained at relatively high levels with low serum creatinine and moderate creatinine clearance levels. Mean survival time increased markedly from 4.1 to 35.2 days by administration of prostaglandin E1. Ischemia-induced acute renal failure is usually accompanied by zonal necrosis of renal tubules prominent in the cortex. However, occurrence of these histologic damages could be virtually prevented by prostaglandin E1 administration (i.e., only minimal tubular necrosis was found in a small area of the cortex). We conclude from this study that postischemic administration of exogenous prostaglandin E1 does provide a certain degree of protection for the kidney, which may have a great clinical implication in improving the success rate of kidney transplantation, especially of cadaver donor kidneys.