Prognostic factors and survival were analysed in 295 patients with metastatic renal cell carcinoma (MRCC), treated with either chemotherapy (1975-1990) or interferon (IFN) (1983-1990). The 3-year survival was 8 and 24% in the chemotherapy and IFN groups, respectively (P < 0.001). In the univariate analysis, age less than or equal to 60 years, prior nephrectomy, more than 1 year since initial diagnosis and treatment for metastatic disease, ECOG performance status 0 or 1, absence of liver metastases, lower erythrocyte sedimentation rate (first hour), and less than or equal to 10% weight loss, within the past 6 months, were correlated with improved survival. Sedimentation rate, performance status and weight loss remained independent prognostic factors from the results of a Cox regression analysis. Three prognostic groups were identified from a combination of these factors. In the poor and intermediate risk groups, no significant survival difference was observed between patients treated with chemotherapy and those treated with IFN. The 3-year survival estimates for good risk patients were 15 and 48% in the chemotherapy and IFN groups, respectively. Therefore, in MRCC, sedimentation rate, performance status and weight loss are easily assessable and reproducible prognostic variables for the identification of risk groups. We hypothesise that IFN may increase survival in good risk patients, but is as ineffective as chemotherapy in poor risk patients with MRCC.