We studied the relationship between clinical stage and tumor infiltrating lymphocytes (TIL) in 26 cases of renal cell carcinoma. In 10 patients, interferon-gamma (IFN-gamma) was administered preoperatively (administration group); 5 patients had low stage (Robson < or = I), and the remaining 5 patients had high stage (Robson > or = II) tumors. The other 16 patients underwent nephrectomy alone without preoperative IFN administration (control group); 11 patients had low stage, and the remaining 5 patients had high stage tumors. Immunohistochemical studies of tumor infiltrating lymphocytes in renal cell carcinoma showed a significantly high incidence of CD3, CD8, CD11b and ICAM-1 in the administration group, while CD4, LFA-1 and Ber-MAC3 were increased without significance (p < 0.05). Concerning clinical stage (Robson), a significant increase in CD3, CD8, CD11b and ICAM-1 was observed in the patients with high-stage tumors in the administration group compared to those in the control group (p < 0.05). This suggested that TIL could be changed by preoperative administration of IFN-gamma.