Twenty consecutive metastatic renal cell carcinoma patients were treated with a combination of recombinant alpha-2a interferon (18 X 10(6) U three times weekly) and vinblastine (0.1 mg/kg every 3 weeks). Two patients (10% response rate; 95% confidence limits 1.23-31.7%) achieved partial response and 11 (55%) stable disease. Toxicity was significant but always acceptable: most frequently, patients complained of fever and flu-like symptoms (18 of 19 patients), fatigue (18 of 19 patients), worsening in performance status (15 of 19 patients), and anorexia (15 of 19). The combination of recombinant alpha-2a interferon and vinblastine is active in renal cell carcinoma.