BACKGROUND Twenty-nine patients with metastatic renal cell carcinoma (RCC) were treated with constant-infusion floxuridine (FUdR, Roche Laboratories, Nutley, NJ). METHODS The initial dosage was 0.075 mg/kg/day for 14 days every 28 days and was increased or decreased by 0.025-mg/kg/day increments at each subsequent cycle until the maximum tolerated dose (MTD) was achieved. RESULTS All patients were fully assessable. One (4%) patient had a complete response, 5 (17%) had a partial response, 13 (50%) had stabilized disease, and 10 (34%) had progressive disease. The treatment-limiting toxic effect was diarrhea, and the median tolerated dosage was 0.1 mg/kg/day for 14 days every 28 days (range, 0.05-0.275 mg/kg/day). Five of the six responses occurred at a dosage of 0.1 mg/kg/day or less, which was achievable in most patients. Patients who reached their MTD without achieving a complete or partial response were switched to circadian-infusion floxuridine to determine whether an increased dose intensity could be administered and whether this would translate into additional responses. A higher median tolerated dosage of 0.15 mg/kg/day was achieved with circadian administration; however, no additional responses were observed. The median survival time was 891 days after the diagnosis of metastatic RCC and 445 days after the institution of floxuridine therapy. CONCLUSIONS Constant-infusion floxuridine is active against metastatic RCC and produces a response rate that appears to be comparable to that of circadian administration of floxuridine.