An immunohistochemical study of the c-erbB-2 protein was conducted on formalin-fixed paraffin-embedded tissue sections from 136 primary gastric carcinomas and 50 metastatic lymph-node tumors obtained at gastrectomy. Expression of the protein was detected in 35 of 136 primary gastric carcinomas (25.7%) and 22 of 50 metastatic lymph nodes (44%). The staining pattern of tumor cells was classified as membranous or cytoplasmic. An immunohistochemical study using serially diluted antibody demonstrated that 82.6% of positive cases in metastatic lymph nodes showed c-erbB-2 immunoreactivity stronger than that in the primary tumors. Membranous staining was stronger than cytoplasmic staining. c-erbB-2 protein of the cytoplasmic as well as membranous types was confirmed to be a 185-kDa whole molecule by immunoblotting. Correlation between the expression of c-erbB-2 protein and clinical and histological parameters was investigated. No significant correlation between 5-year survival rate of patients and expression of c-erbB-2 protein was found. In the poorly differentiated carcinoma group possessing c-erbB-2 protein, overall survival was significantly shorter than in cases without protein expression (p < 0.01). We conclude that c-erbB-2 protein is not a useful prognostic indicator in gastric carcinomas.