c-erbB-2 gene amplification was examined by slot blot hybridization using DNAs extracted from formalin-fixed and paraffin-embedded tissues of primary gastric carcinomas. Eleven of the 82 carcinomas (13.4%) exhibited amplification. Twenty-eight carcinomas (34.1%) expressed c-erbB-2 protein immunohistochemically. All of the tumors with amplified c-erbB-2 genes had expression of c-erbB-2 protein. The incidence of diploid and aneuploid tumors with c-erbB-2 gene amplification was similar. The survival rate was significantly lower in cases with c-erbB-2 gene amplification. Furthermore, patients with tumors showing a combination of c-erbB-2 gene amplification and DNA aneuploidy had the poorest prognosis. c-erbB-2 gene amplification may be an important prognostic indicator in gastric carcinomas.