E-cadherin (E-CD) is a transmembrane glycoprotein involved in intercellular adhesion. A loss or reduction in E-CD expression has been linked to the invasive phenotype of a wide variety of human neoplasms, including bladder tumors. The objective of this study was to compare the E-CD expression at different depths of tumor invasion below the bladder's basement membrane in high- and low-grade urothelial carcinomas to investigate whether deeper tumor invasion and higher-grade invasive urothelial carcinomas are associated with decreased E-CD expression. E-cadherin staining was performed on 29 formalin-fixed, paraffin-embedded sections from high- and low-grade urothelial carcinoma specimens using an automatic immunohistochemical stainer. The sections were divided into three categories according to the depth of invasion below the basement membrane: upper, middle, and lower. The percentage and intensity of E-CD cell membrane staining for the three categories were calculated using a quantitative automated cellular imaging system. The percentage of cells that stained for E-CD was 82.6% +/- 1.4% (mean +/- SD) in the upper layer, 59.6% +/- 2.2% in the middle layer, and 29.4% +/- 2.7% in the lower layer. The intensity of E-CD expression was 64.7 +/- 3.2 units in the upper layer, 43.3 +/- 2.9 units in the middle layer, and 26.1 +/- 3.1 units in the lower layer. There were significant differences between the three layers in both the percentage and intensity of cellular E-CD staining (P<.05). Normal urothelium, high-grade urothelial dysplasia/carcinoma in situ, and superficial noninvasive papillary urothelial carcinoma maintained E-CD expression. However, once malignant cells infiltrated through the basement membrane, E-CD expression decreased. The more poorly differentiated urothelial carcinoma, the deeper the nests, and the smaller the clusters of neoplastic cells within the tumor were, and the more decrease in E-CD expression noted. The degree of decreased E-CD expression was directly proportional to the degree of tumor differentiation and depth of infiltration in invasive urothelial carcinoma. Down-regulation of E-CD may be one of the pathways responsible for tumor differentiation and may promote deeper invasion in urothelial carcinomas.