The present study was designed to clarify whether bel-xL is involved in the development of carcinoma in the stomach. Levels of bel-xL and bc1-2 mRNA were determined by a reverse-transcription/polymerase-chain reaction in endoscopic gastric biopsy specimens from 10 control subjects, 11 patients with adenomas and 14 patients with carcinomas. In 6 of 11 adenomas, 5 of 8 early carcinomas and 3 of 6 advanced carcinomas, the bel-xL gene was over-expressed. In carcinomas, overexpression of the bel-xL gene was observed in 6 of 9 intestinaltype carcinomas and 2 of 5 diffuse-type carcinomas. No correlation was observed between bel-xL and bc1-2 gene expression. In cases in which the bel-xL gene was over-expressed, an apparent increase in the protein level of Bcl-xL was observed by immunoblot analysis and intense Bcl-x immunoreactivity was detected immunohistochemically within the tumor cells. In conclusion, we showed that bel-xL is over-expressed in gastric carcinomas at both the RNA and protein levels, suggesting that overexpression of bel-xL may play a role in gastric carcinogenesis. © 1996 Wiley-Liss, Inc.