We treated 19 patients with progressive metastatic renal cell carcinoma with continuous infusion of 5-fluoro-2-deoxyuridine, 52 per cent of whom had previously received and failed chemotherapy. Implantable pumps were used for automatic drug delivery. 5-Fluoro-2-deoxyuridine was infused continuously for 14 days at monthly intervals. The starting dose was 0.15 mg. per kg. per day (intravenous) or 0.25 mg. per kg. per day (intra-arterial). Intravenous doses were increased or decreased in increments of 0.025 mg. per kg. per day as permitted by toxicity. Abdominal pain, diarrhea and mucositis limited the intravenous infusion, while malaise, anorexia and hepatic function abnormalities limited intra-arterial infusion. Of 18 evaluable patients we observed 1 complete, 4 partial (objective response rate 28 per cent) and 2 minor responses. The duration of response ranged from 2 to greater than 18 months. During a median follow up of 7.5 months (range 2 to 21 months) only 4 of the 18 patients had objective tumor progression. Over-all survival for the 19 patients was 94 per cent. Continuous infusion of 5-fluoro-2-deoxyuridine may be effective for the treatment of progressive renal cell carcinoma.