Background. Cancer-associated, major histocompatibility complex (MHC-restricted peptide antigens have been elucidated in human melanomas and ovarian, breast, and renal carcinomas; but relatively little is known about lung cancer antigens. Methods. To work toward delineation of lung cancer-associated antigens, we developed tumor infiltrating lymphocytes (TILs), peripheral blood mononuclear cell-derived cytolytic T cell lines (CTL), autologous lung cancer cell lines, and normal lung cell lines from 17 patients undergoing lung cancer resections. The TILs and CTL lines were subsequently evaluated for markers of activation and specific lysis of autologous or allogeneic lung cancer cell lines or both. Results. Freshly isolated TILs contained a more activated T cell population compared with the patients' peripheral blood T cells as evidenced by an increased expression of HLA-DR, CD25, and CD45RO. TILs isolated from 15 patients lysed allogeneic lung cancer lines. TILs lysed autologous lung cancer but not autologous normal lung or Epstein-Barr virus transformed B cell lines (B-LCL) in 4 of 8 cases tested, suggesting tumor specificity. A CTL line (RHPBL57.1) was generated from peripheral blood mononuclear cells of an HLA-A24+ patient by stimulation against an established HLA-A24+ allogeneic lung cancer cell line. RHPBL57.1 lysed the lung cancer cell line in an HLA-A24- restricted manner. Moreover, RHPBL57.1 specifically lysed autologous B-LCL pulsed with peptides, eluted from MHC class I and isolated from the HLA-A24+ lung cancer cell line. Conclusions. TILs isolated from patients with lung cancer are predominantly an activated population of T cells with evidence of tumor and MHC class I-restricted lysis. Furthermore, we provide evidence for a lung cancer-associated, MHC class I-bound peptide antigen(s) that reconstitutes the epitope recognized by a lung cancer specific CD8+ T cell line derived from a patient with lung cancer.