Expression of the nm23 and E-cadherin proteins has been studied in a number of tumors. Reduced expression of the nm23 and E-cadherin proteins seems to be associated with metastasis or disease progression in some tumors, including breast carcinoma. To assess the role of nm23 and E-cadherin in tumor differentiation and metastasis of breast carcinoma, immunohistochemical staining for the nm23 and E-cadherin proteins was performed in paraffin embedded tumor samples from 86 breast carcinomas. The results were as follows: 1) Expression of the nm23 protein in breast carcinoma was strong positive in 32 cases (37.2%), weak positive in 26 cases (30.2%), and negative in 28 cases (32.6%) of the cases. Expression of the nm23 protein in breast carcinoma decreased according to histological grade and lymph node metastasis, but was not statistically significant. 2) Expression of the E-cadherin protein in breast carcinoma was strong positive in 50 cases (58.1%), weak positive in 24 cases (27.9%), and negative in 12 cases (14%) of the cases. Expression of the E-cadherin protein in breast carcinoma decreased according to histological grade and lymph node metastasis, but was not statistically significant. 3) There was a statistically significant correlation between the expression of the nm23 protein and the E-cadherin protein in breast carcinoma (p<0.05). These results suggest that the expression of the nm23 and E-cadherin proteins is related to tumor differentiation, and may also be an useful prognostic factor in breast carcinoma.