The immunological properties of tumour-infiltrating (TIL) and peripheral blood lymphocytes (PBL) from 29 patients with renal cell carcinomas were characterized with respect to their phenotypic expression and cytokine production. TIL were isolated from mechanically disaggregated tumor material and PBL from peripheral blood by gradient centrifugation. To eliminate all non-lymphoid cells, CD3-positive cells were specifically separated from these cell fractions with anti-CD3 magnetic beads. These pure CD3-positive PBL (CD3+PBL) and TIL (CD3+TIL) were cultured with pokeweed mitogen and the levels of the cytokines interleukin-1alpha (IL-1 alpha), IL-1 beta, IL-2, interferon gamma (IFNgamma), and tumor necrosis factor alpha (TNFalpha) measured in the 4-day post-inductional cell culture supernatants. In all cell cultures a wide range of cytokine values was found, indicating a large variation in the immunological activity of the lymphocytes of each individual. When the cell cultures of the CD3+TIL and CD3+PBL were compared in each patient similar values for IL-1 alpha, IL-1 beta, IFNgamma and TNFalpha were found. However CD3+TIL produced significantly lower levels of IL-2 than CD3+PBL upon mitogenic stimulation. This may be due to a lower CD4/CD8 ratio in the CD3+TIL as compared to the CD3+PBL. These results suggest that there are no fundamental qualitative and quantitative differences in the lymphokine-producing capacity of CD3+TIL and CD3+PBL derived from patients with renal cell carcinomas.