The treatment of patients with metastasized renal cell carcinoma by biological response modifiers such as interferon (IFN), interleukin-2 (IL-2) and tumor necrosis factor (TNF) should at present only be carried out in prospective studies since there are still no generally accepted treatment regimens for these substances. In addition, one must remember that only interleukin-2 has been approved for the treatment of renal cell cancer by the Bundesgesundheitsamt (Federal Health Authority) in Berlin. Regarding interferons, IFN-alpha seems to be the most suitable substance for the treatment of renal cell cancer. However, objective response rates (almost exclusively partial responses) can only be expected in about 15% of the cases. By combining IL-2 with lymphokine-activated killer cells or IFN-alpha, objectively assessed remissions can be found in 35%. The approximate complete-response rate using this form of treatment, however, is in the range of 10%.