Acute renal failure developed in nine of 78 patients who were subjected to hepatic artery ligation for nonresectable and extensive malignant tumor of the liver. Of those nine, six had hepatomas, one cholangiocarcinoma, one metastatic islet-cell carcinoma and one metastatic melanoma. Preoperative renal function as reflected in blood-urea-nitrogen and serum creatinine values was within normal limits. There were marked elevations of serum glutamic-oxalacetic transaminase and lactic dehydrogenase levels after hepatic artery ligation, an indication of massive ischemic injury of the tumor and the liver. A diagnosis of acute renal failure was established within 14 to 70 hours after hepatic artery ligation. In five patients, oliguric renal failure developed, and in four, high urinary output renal failure. In only three patients did systemic hypotension and hypovolemia precede acute renal failure. Seven of the nine patients died. Postmortem examination was done in five patients, and in only two was there evidence of renal tubular necrosis. The factors contributing to acute renal failure appear to be extensive involvement of the liver by tumor, presence of ascites and jaundice, occlusion of the portal vein and hyperuricemia. The presence of any one of the foregoing contraindicates the procedure.