Alpha Interferon therapy was applied to 12 previously untreated patients with metastatic renal cell carcinoma and measurable disease. Eleven patients had been previously nephrectomised. Seven patients had only lung metastases, 4 patients had other sites of metastases and one patient had both lung and other sites of metastasis. Interferon alpha- 2b was given as 10 mU three times a week subcutaneously. Response was evaluated at least 2 months later. There were 2 complete and 5 partial responses in the 7 patients who had only lung metastasis. The rest tumors were resected in 2 patients with partial response and no other evidence of disease. One patient with sole abdominal lymph node metastasis also showed partial response. There was no objective response in 2 patients with bone metastases but the analgesic need was decreased in both of them. Interferon therapy continued for 6 to 12 months in responders. The median time to progression was 10 months. There was no severe toxicity other than the flulike syndrome which was seen in almost all cases. In conclusion, Interferon therapy is a treatment modality that could be tried in renal cell carcinoma, especially in patients with lung metastases.