Objective To investigate the mechanism of renal cell carcinoma (RCC) in affecting the immune system of the host. Methods FasL expression and the apoptosis of tumor infiltrating lymphocytes (TIL) were examined by immunohistochemical technique in 44 cases of RCC.FasL function was assessed by coculture assays in vitro using the renal cancer cells 786 0 or GRC 1 and the Fas sensitive Jurkat T cells. Results (1)FasL expression rate in RCC (46.5%) was higher than that in the normal kidney tissues (23.2%, P