One hundred and thirty cases of gastric carcinoma were immunohistochemically examined in regard to the expression of c-erbB-2 protein. C-erbB-2 protein was expressed in 36 cases. Number of cases in the differentiated type was 31 out of 78 cases, whereas that of the undifferentiated type was 5 out of 52 cases. And there were 2 positive cases among 26 cases of early type, whereas there were 34 positive cases of advanced type. In 60 cases of differentiated and advanced type carcinomas, the positive staining related significantly with tumor size, infiltrative growth pattern and peritoneal dissemination. The 5 year survival rate after curative resection was analyzed among the patients with differentiated type carcinoma. The rate of 39 negative cases was 78.0%, whereas it was 46.4% in 20 positive cases. These results indicate that the expression of c-erbB-2 protein in gastric carcinoma may be related to the degree of differentiation and the stage of progression, and further, it seems well correlated with the biological behavior of the differentiated but advanced carcinoma as shown by the positive tendency in larger size, deeper infiltration and shorter 5 year survival.