A phase II multiinstitutional clinical trial was conducted to evaluate the safety and efficacy of the subcutaneous outpatient administration of recombinant human interleukin-2 and alpha-interferon in patients with progressive metastatic renal cell carcinoma. One hundred and forty-five patients were entered on this study between October 1989 and May 1991. Among 134 patients evaluable for treatment response, there were six complete (4.5%) and twenty partial (14.9%) responders, with an overall response rate of 19.4% (95% confidence interval, 13-26%). The median duration of complete remissions was 228 (range 51(+)-520+) days; the median duration of partial tumor regressions was calculated at 226 (range 112-473+) days. The overall median survival from start of therapy was 14.2 (range 1-23+) months. Fever, chills and general fatigue occurred in the majority of patients treated and were measured at grade II, III and IV in up to 55%, 24% and 3% of all evaluable patients, respectively. Three patients each developed grade III hypotension, dyspnea and diarrhea; two patients each had grade III and grade IV elevations of alkaline phosphatase; two and one patients respectively, exhibited grade III anemia and grade IV thrombocytopenia; two patients experienced severe cutaneous toxicity. The majority of patients received treatment in the outpatient setting. In summary, the outpatient use of subcutaneous interleukin-2 and alpha-interferon was effective in patients with advanced metastatic renal cell carcinoma; it was associated with less toxicity and thus, could improve the therapeutic index of interleukin-2 based biologic therapy when compared against high dose intravenous therapy.