We studied the effect of treatment on tumour response and survival of 76 evaluable patients with renal cell carcinoma, treated in this unit over a 12-year period. For the purpose of this study patients were classified into three groups according to the treatment they received: (a) 22-patients were evaluable for treatment with alpha-interferons; (b) 20 for treatment with immune modulation, other than interferon; (c) 34 patients received hormone treatment, chemotherapy or had no systemic treatment. Objective tumour regressions were observed only among patients who received interferon. No difference in overall survival from first diagnosis or from diagnosis of Stage IV disease could be demonstrated in these three groups. Alpha-Interferons are the first agents to induce clinically meaningful and reproducible regression of metastases in renal cell carcinoma. This treatment, however, has not been shown to have a major impact on survival.