Twenty patients (6 females and 14 males), age range 36-70 years-old, with metastatic renal cell carcinoma (MRCC), received interferon alpha-2b (IFN-A) 10 x 10(6) units/day IM for 5 days followed by continuous i.v. infusion of interleukin-2 (IL-2) 18 x 10(6) units/day for 5 days. The median follow-up was 10 months. We observed four partial responses (20%), 13 stable (65%) and three progressive diseases (15%). The mean CD4/CD8 ratio, obtained before therapy in patients with MRCC, was compared with CD4/CD8 ratio in 51 patients with different advanced malignancy and in patients with no cancer. The CD4/CD8 ratio was higher in patients with MRCC (2.55) than in other cancers (1.474) and than in populations with no cancer (1.66 x chi 2 = 17,378). The surface phenotypes of peripheral lymphocytes were analysed by cytofluorometry in patients with MRCC during and after treatment with IFN-A and IL-2. Immune modulatory effects of therapy immediately induced a decrease of different sub-populations of lymphocytes except CD25+. Far from the first course, a rise in lymphocyte count was observed. The proliferation effect was as follows: CD4+, CD8+, CD4+ CD45RA- and CD16+ CD8- cells. Far from the second and 3rd course, the sub-populations of lymphocytes decreased, except the CD4+ and CD4- CD45RA+ cells. The CD4/CD8 ratio increased progressively during treatment. Before each course, the CD4/CD8 ratio of patients with response to treatment was higher than the CD4/CD8 ratio of patients with no response. Results were non-significant due to the small number of subjects with responses in this study.