Twelve patients with metastatic renal cell carcinoma were entered into a phase-2 study of an 8-week course of interferon (INF) therapy. INF was given subcutaneously at a dose of 3 mu, three times per week. The patients were WHO performance status 0–2. A complete response was obtained in two patients (17% response rate), which has been maintained at 23 and 45 months. One of these patients presented with cranial and lung metastases and received cranial irradiation and decradron concurrent with INF. The toxicity of INF has been low. The optimal duration of INF therapy warrants further evaluation.