PURPOSE: The cDNA microarray provides a powerful alternative with an unprecedented view in monitoring gene- expression levels and leads to discoveries of regulatory pathways involved in complicated biological processes. Our aim is to explore the different gene-expression patterns in gastric adenocarcinomas. MATENRIALS AND METHODS: By using a cDNA microarray representing 4,600 cDNA clusters, we studied the expression profiling in 10 paired gastric adenocarcinoma samples and in adjacent noncancerous gastric tissues from the same patients. Alterations in the gene-expression levels were confirmed by Vsing Northern blots and reverse-transcription PCR (RT-PCR) in all of 4 randomly selected genes. RESULTS: Genes those were expressed differently in cancer ous and noncancerous tissues were identified. 44 (of which 26 were known) and 92 (of which 43 were known) genes or cDNA were up- and down-regulated, respectively, in more than 80% of the gastric adenocarcinoma samples. In cancer ous tissues, genes related to gene/protein expression, cell- cycle regulation, and metabolism were mostly up-regulated whereas genes related to the oncogene/tumor suppressor gene, cell structure/motility, and immunology were mostly down-regulated. The semi-quantitative RT-PCR results for the four genes we tested were consistent with the array findings. CONCLUSION: These results provide not only a new molecular basis for understanding the biological properties of gastric adenocarcinomas but also a useful resource for future development of therapeutic targets and diagnostic markers for gastric adenocarcinomas.