In a phase II clinical trial 23 patients with metastatic renal cell carcinoma were treated with a cyclic regimen of interferon alpha-2b (IFN-alpha). To these 23 patients IFN-alpha at a dose of 10 MU/m2 body surface was applied subcutaneously on 5 consecutive days every 4 weeks. In 12 out of these 23 patients tumor nephrectomy preceded this treatment. The mean follow-up period was 13.6 (range 2-36) months. No complete remission was achieved in any of the patients. One patient with lung metastases revealed a partial response for 19 months. Stable disease lasting 4 to > 36 (mean: 18.7) months was seen in 7 cases. Progressive disease was observed in 15 patients. Only slight side effects were noted, consisting of a maximum toxicity of grades II (n = 20) and III (n = 3) according to the WHO classification. Five out of 8 patients with partial responses or stable disease showed a long-lasting stabilization (> 12 months) of the disease with a good quality of life. In summary, in advanced renal cell carcinoma patients, the objective response rate of a cyclic treatment with IFN-alpha is rather low. However, a long-lasting stabilization of the disease including a good quality of life can be expected in a modest proportion of the patients.