A prerequisite to the developement of an efficient cell and/or gene therapy for lung cancer is a precise characterization of the inflammatory cell populations spontaneously present in the tumor stroma associated with this cancer. This study was designed to define the cytotoxic potential and the relationship with stroma development of tumor infiltrating lymphocytes (TIL) and tumor associated macrophages (TAM). Tumor samples from 48 patients undergoing surgery for non-small cell lung cancer (NSCLC) were analyzed, by immunohistochemistry and in situ hybridization, with a panel of antibodies and probes specific for cell proteins linked to cytotoxicity, cytokines, and growth factors, and the replication status of TIL and TAM was evaluated by in vivo 5-bromodeoxyuridine incorporation. It was shown that, in NSCLC: (1) tumor stroma inflammatory cells are mainly TIL (approximately 2/3) (among them, 80 % are T-cells) and TAM (approximately 1/3), with almost no natural killer (NK) cells, and a few dentritic cells; (2) TAM and TIL are poorly replicating, but mainly recruited to the tumor stroma; (3) more than half TAM show an antibody-dependent cytotoxic potential, and one third of T-cells are TIA-1 positive CD8 activated cytotoxic lymphocytes; (4) cancer cells from only a few tumor express HLA class I and II antigens; (5) TAM production of cytotoxic cytokines [interleukin-1alpha (IL-1alpha), IL-1beta, IL-6, tumor necrosis factor-alpha (TNF-alpha)] and of transforming growth factor-beta1 (TGF-beta1) is low, in contrast to their strong release of platelet-derived growth factor (PDGF). We concluded that, in NSCLC, TIL cytotoxicity is likely to be low because of a poor class I MHC expression by tumor cells, and TAM low production of cytotoxic cytokines is a major limit to their possible cytotoxic activity. In contrast, TAM may favor tumor progression by contributing to tumor stroma formation and angiogenesis through their release of PDGF, in conjunction with TGF-beta1 production by tumor cells.