In a variety of human cancers, the presence of tumor-infiltrating T lymphocytes (TILs) is associated with tumor regression and favorable prognosis. Local interferon (IFN)-gamma secretion from activated T cells is supposed to induce a specific immune response leading to tumor-specific cytotoxicity. Nonetheless, significance and properties of TILs still remains controversial in lung cancer patients. We determined CD8+ T cell counts in 31 patients with non-small cell lung cancer (NSCLC) by immunohistochemistry, and assessed T-cell immune activation status in a subset of patients by measuring IFN-gamma mRNA expression by quantitative PCR (TaqMan). Semi-quantitative immunohistochemical analysis revealed significantly higher CD8+ T cell counts within the tumor as when compared to the invasive margin. CD8+ T cells immune activation status, represented in the IFN-gamma/CD8 mRNA ratio, correlated with the median number of CD8+ T cells presented at the tumor-host interface. Neither tumor histology and grade, nor CD8+ T cell counts and IFN-gamma/CD8 ratio could demonstrate an influence on overall survival in these patients. Our results indicate that CD8+ T cells infiltrating the tumor cell nests may be inadequately activated and thus incapable of mounting an effective anti-tumor immune response.