Advanced renal cell carcinoma was treated by transcatheter embolization with radioactive seeds. There were 14 patients with nonresectable or metastatic disease (stage IV) and 8 with stage II tumors treated. In 8 patients the tumor was implanted with radon seeds, complemented by 2,500 rad of external beam therapy, and 10 were treated by embolization with 125iodine seeds. The total dose delivered ranged form 1,600 to 14,000 rad. Several patients also had intra-arterial chemotherapy. Survival was improved over previously reported studies: 13 of 22 (59 per cent) at risk for 2 years and 5 of 15 (33 per cent) for 5 years. Distant metastases did not resolve but significant local palliation was achieved. Tumor size decreased in all patients, 8 of whom subsequently underwent nephrectomy. Other local effects included pain control (10 per cent), weight gain (75 per cent) and control of hemorrhage (88 per cent). Toxicity was minimal and consisted of mild nausea or pain. This approach, using a low energy emitter, allows selective high dose radiation of the tumor, while sparing the adjacent normal tissues. In contrast to renal artery occlusion with inert embolic material, subsequent nephrectomy in patients with disseminated disease is not necessary. Transcatheter embolization with radioactive seeds should be considered a reasonable palliative procedure in patients with nonresectable primary renal cell carcinoma.