Protein expression levels of E-cadherin and beta-catenin were examined in 39 primary and 10 metastatic ovarian carcinoma to elucidate the role of these molecules in the extension of ovarian carcinoma by immunohistochemistry. Twenty-two of 39 (56%) ovarian carcinomas were preserved type and 17 of 39 (44%) were reduced type of E-cadherin. In contrast, 36 of 39 (92%) ovarian carcinomas were preserved type and 3 of 39 (8%) were reduced type of beta-catenin. E-cadherin expression in well-differentiated carcinoma was higher than that in moderately/poorly-differentiated carcinoma (p<0.05). Interestingly, 6 of 10 (60%) peritoneal metastatic lesions resulted in the reduced expression of E-cadherin compared with primary lesions. In contrast, only 2 of 10 (20%) metastatic lesions showed reduced expression of beta-catenin compared with primary lesions. Mutation of exon 3 of beta-catenin gene was rare (3%, 1/39) in carcinoma. These results suggested that the cell adhesion molecule E-cadherin might play an important role in the formation of peritoneal metastasis. In contrast, beta-catenin is not a good indicator of metastasis in human ovarian carcinoma.