Internal radiation therapy with transarterial injection of iodine-131-labeled iodized oil (Lipiodol Ultra-Fluide [LUF]) was evaluated in 15 patients with hepatocellular carcinoma and eight with hepatic metastases. Five patients with hepatocellular carcinoma received more than one injection. Treatment tolerance was excellent, as assessed clinically and by means of liver function tests. An analgesic effect was noted in the two patients with painful hepatocellular carcinomas. Serum alpha 1-fetoprotein levels dropped rapidly in 11 of the 12 patients with elevated basal values. An average reduction in tumor size of 50% was observed in the nine cases followed up with computed tomography. After 5-12 months of follow-up, six of the 15 patients with hepatocellular carcinoma were alive. Two of them had undergone liver transplantation. Histologic examination of one of the livers, removed 3 months after a third injection, revealed microscopic features highly suggestive of radiation effect in LUF-containing areas. In the group with widespread hepatic metastases, no objective response was noted, except for an analgesic effect in three cases.