The purpose of this study is to evaluate the clinical significance of E-cadherin expression in lung cancer. E-cadherin expression was detected by immunohistochemistry using a monoclonal antibody (HECD-1). Strongly positive (++) E-cadherin tumors were classified as a type of preserved E-cadherin expression (Pr type), while the others (+, - tumors) were classified as a type of reduced E-cadherin expression (Rd type). The frequency of Pr type in squamous cell carcinomas (59.0%) was higher than Rd type. However, in adenocarcinomas, the frequency of Rd type was higher than Pr type. E-cadherin expression pattern was significantly correlated with differentiated state (Pearson correlation coefficient 0.394, p<0.001). E-cadherin expression of well-differentiated tumors was more frequently preserved than that of poorly differentiated tumors (60.0% vs. 25.9%). With regard to the correlation between E-cadherin expression and stages of lymph node metastasis in non-small cell lung cancers, the percentage of tumors with Pr type E-cadherin expression declined from 66.3% (< or = N1) to 38.6% (> or = N2), indicating that loss of E-cadherin expression is responsible for acquisition of invasive potential of lung cancer as well as the possible role of E-cadherin in the histological differentiation of lung cancer.