Twenty patients with histologically confirmed metastatic or recurrent renal carcinoma were treated in a phase II study with alpha-interferon (2-5 x 10(6) U/m2 subcutaneously, 3 times a week). Nineteen patients had multiple sites of disease and 18 had previously undergone nephrectomy; 9 had an ECOG performance status of 0.1, and 11 had a performance status of 2-3. There was one partial response, yielding an overall response rate of 5%. Treatment was well tolerated, although 7 patients developed influenza-like symptoms, and in 2 cases this was sufficiently severe for the patients to request cessation of treatment. As a single agent at this dose schedule, alpha-interferon has minimal activity in the treatment of renal carcinoma and cannot be recommended as standard therapy. The difference in outcome between this and some published series may reflect the stringent requirement for histological proof of the presence of metastases.