The MAGE, BAGE, and GAGE genes code for distinct antigens that are recognized by autologous cytolytic T lymphocytes. We investigated the expression of these genes in both cell lines and surgical samples of gastric carcinoma, using reverse transcription-PCR. Furthermore, the induction of these genes by 5-aza-2'-deoxycytidine (DAC), a demethylating agent, was also examined in several cell lines. Of 11 cell lines, BAGE, GAGE1-6, GAGE1-2, MAGE-1, and MAGE-3 were detected in 7 (64%), 4 (36%), 3 (27%), 8 (73%), and 8 (73%) cell lines, respectively. After the in vitro treatment of the negative cell lines with DAC, the expression of these genes became positive in 46 to 91% of these cell lines. No expression of these genes was seen in any of the 57 samples of normal gastric tissue. In contrast, the tumor tissue samples expressed BAGE, GAGE1-6, GAGE1-2, MAGE-1, and MAGE-3 in 13 (23%), 9 (16%), 6 (11%), 25 (44%), and 23 (40%) tissue samples, respectively. Thus, at least one of these genes was expressed in 35 (61%) of 57 carcinomas. An analysis of the relationship between clinicopathological factors and the expression of these genes revealed that either BAGE or one of these genes was more frequently expressed in histologically intestinal-type than in diffuse-type carcinomas. Our results suggest that, because of the higher expression of these genes and the possible induction of these genes by DAC, patients with gastric carcinoma may, therefore, be potential candidates for tumor-specific immunotherapy directed against these antigens.