Tumor necrosis factor alpha (TNFalpha) and TNFalpha receptor mRNA expression, the effects of TNFalpha on DNA synthesis and cell proliferation as well as its effects on interleukin-6 (IL-6) production and expression in renal cell carcinoma (RCC) were studied using RCC cell lines. The effects of TNFalpha on DNA synthesis and IL-6 production were also studied using short-term established RCC cell lines. A total of 8 cell lines, 4 RCC cell lines (RC-2, RGB, 14T, 4T) and 4 cell lines established at our laboratory (OCUU-1, 2, 4, 5), as well as 10 short-term established RCC cell lines were used. When TNFalpha and TNFalpha receptor mRNA expression was examined by RT-PCR, p55 TNF receptor mRNA expression was observed while TNFalpha and p75 TNF receptor mRNA expression was not observed in all cell lines. When the effects of TNFalpha on DNA synthesis were studied by [3H]-thymidine incorporation assay, DNA synthesis was induced in RGB, 14T, 4T, OCUU-2 and OCUU-4 by adding 10 and 100 pg/ml of TNFalpha while it was not induced in RC-2 and OCUU-5 at all concentrations. When its effects on cell proliferation were evaluated by MTT assay, cell proliferation was observed in RGB, 14T and 4T at TNFalpha concentration of 10 pg/ml and in RGB, 14T, 4T, OCUU-4 and OCUU-5 at TNFalpha concentration of 100 pg/ml. However, cell proliferation was not detected in RC-2 and OCCU-2 at any concentration. When the effects of TNFalpha on IL-6 production were studied by ELISA, IL-6 production was induced in RC-2, RGB, 14T, OCUU-1, OCUU-2 and OCUU-5 while not in 4T and OCUU-4. When its effects on IL-6 expression were examined by Northern blot analysis, the results were similar to those obtained by ELISA. As for the 10 short-term established RCC cell lines, DNA synthesis and IL-6 production were induced with the addition of TNFalpha. These results suggested that TNFalpha induced cell proliferation in RCC.