The expression of cyclin E in human gastric adenomas and adenocarcinomas was examined immunohistochemically to elucidate the role of cyclin E in stomach carcinogenesis. The expression of cyclin E was detected in 49% (90/182) of the adenomas and 59% (260/439) of the adenocarcinomas. The incidence of strongly positive cases (overexpression of cyclin E) was significantly higher in the adenocarcinomas (29%; 128/439) than in the adenomas (4%; 8/182) (p < 0.01). The incidence of the cyclin E expression showed a tendency to be higher in deeply invasive carcinomas and in the cases with lymph node metastasis, while the incidence did not differ among histological types. The expression of cyclin E was significantly correlated with the proliferative activity of the tumor cells measured by KI-67 antigen expression (p < 0.01). It was also correlated with the abnormal accumulation of p53 protein in the tumor cells (p < 0.01). These results suggest that overexpression of cyclin E and subsequent deregulation of the cell cycle may confer the development and progression of the gastric carcinomas.