Immune recognition of human cancers except melanoma is not well understood at either the cellular or the molecular level. We demonstrate in this study the existence of HLA class-I-restricted and tumor-specific CTL in IL-2-activated TIL (tumor-infiltrating lymphocytes) of all 4 gastric cancer patients tested. We established HLA A2-restricted and adenocarcinoma-specific CTL in 2 HLA A0201+ patients, and HLA A2402-restricted CTL recognizing both adenocarcinoma and squamous-cell carcinomas (SCC) in the 2 remaining HLA A2402+ patients. Further, HLA A3101-restricted and adenocarcinoma-specific CTL were established in 1 of the 2 HLA A2402+ patients who had HLA A3101 allele. HLA A2-, A2402- and A3101-restricted CD8+ CTL clones were established from these parental CTL lines. The 2 HLA A2-restricted CTL lines lysed 8 of 13 HLA A2+ adenocarcinoma cell lines established from different organs (stomach, colon, lung and breast) with different subtypes (HLA A0201, A0206 and A0207). The HLA A2-restricted CTL line recognized 9 and 6 different HPLC fractions of peptides eluted from the HLA A0201+ breast and HLA A0201+ colon adenocarcinoma cell lines, respectively. Allele-specific deletion of HLA A2 or A24 molecules was observed in some tumor lines that were not susceptible to lysis by the CTL lines. These results suggest that TIL of gastric cancer possess CTL recognizing different peptide antigens binding to different HLA-A alleles that are widely expressed on adenocarcinomas and also, to some extent, on SCC from different organs.