Risk factors may influence not only prognosis in metastic renal cell carcinoma but also probability of response to immunotherapy. Response of patients treated with inhalation of interleukin-2 (IL-2), which can be offered to those not suitable for systemic therapy, was compared to risk factors. We report on 116 patients who used inhaled IL-2 and were treated in different protocols with natural, recombinant glycosylated and recombinant non-glycosylated.