The purpose of this study was to determine the efficacy and safety of a new high-dose interleukin (IL)-2 regimen, given two days a week, for renal cell carcinoma. One hundred and four patients received IL-2 as a continuous i.v. infusion for 48 h at a daily dose of 24 x 10(6) IU/m2/day for 5 consecutive weeks. Patients were assessed for efficacy 4 and 8 weeks after the end of therapy, and patients who stabilized or responded received maintenance therapy with the same regimen. An objective clinical response was observed in 20 patients (complete in four, partial in 16). The dose of infused IL2 was significantly higher in the responders than in the nonresponders (p < 0.05). Clinical responses were significantly associated with a sedimentation rate of < 20 (p = 0.02), but no other prognostic factor was identified. Mean survival was 13 months. Grade 3 and 4 toxicities were rare, except for hypotension (58% of patients), the main dose-limiting toxic effect. Overall, 83% of the planned dose of IL-2 was given. IL-2 given 2 days a week is active in metastatic renal cell carcinoma and well tolerated.