1. Only clear cell and chromophilic carcinomas of the kidney exhibit a considerable lymphocytic infiltration which is compatible with some immunological responsiveness. Chromophobic carcinomas and benign oncocytomas seem to be immunologically reactive. This reflects the different antigen spectrum and histogenesis of these tumors (Störkel and Jacobi, 1989). Clear cell and chromophilic carcinomas are derived from the proximal tubule and chromophobic carcinomas and oncocytomas from the collecting duct. 2. The tumor periphery seems to be the place of greatest immunological importance, as basic requirements of a sufficient lymphocyte/tumor cell interaction can only be expected there. If these data are taken into account for a therapeutical approach with biological immune modifiers the size of the tumor (tumor burden) and proliferation index must be considered too. This might be a likely explanation for the positive effect of inhaled interleukin-2 on lung metastasis in renal cell cancers. Harvesting of tumor infiltrating lymphocytes for therapeutical purposes should take these findings into account. 3. In spite of dense lymphocytic infiltration only 3% of the tumor infiltrating lymphocytes exhibit the activation marker CD 25. There seems to be a sufficient T cell locomotion in renal cell carcinomas but an insufficient T-cell activation. Whether this fact is induced by lacking cytokine stimulation of involved lymphocytes or by still unknown mediators of the tumor cells is not yet known and needs further investigation. 4. Clear cell carcinomas exhibit most adhesion molecules and the highest amount of infiltrating cytotoxic T-cells and natural killer cells.(ABSTRACT TRUNCATED AT 250 WORDS)