The mRNA expression of the cytokines IFN-γ, IL-10 and TNF-α and the proapoptotic factor Fas ligand (FasL) was compared in freshly isolated CD4+and CD8+tumour-infiltrating lymphocytes (TIL) and simultaneously obtained autologous CD4+and CD8+peripheral blood lymphocytes (PBL) from 20 patients with renal cell carcinomas (RCC). The gene discussed is IL10; the disease is renal cell carcinoma.