AIM: To assess the expression of α-catenin in gastric carcinoma and to determine the role of α-catenin expression in gastric carcinogenesis.METHODS: α-catenin expression was assessed by semi quantitative reverse transcriptase-polymerase chain reaction and immunohistochemical staining in 49 gastric carcinomas,26 adjacent non-cancerous mucosae, and gastric biopsy specimens from 11 healthy controls.RESULTS: mRNA levels of α-catenin were reduced or absent in 34 of 49 (69%) gastric carcinoma tissues and in 5 of 26 (19%) tumor-free gastric mucosae of carcinomapatients, respectively. Of the carcinoma samples with altered α-catenin mRNA levels, α-catenin expression was negative in 20 and decreased in 14 cases. Up to 69% of tumors were stained abnormally for α-catenin. Of the 34 cases whose mRNA expression of α-catenin was reduced, 32 (94%) showed abnormal immunostaining patterns, while only 2 showed a normal α-catenin expression. The frequency of reduced expression of α-catenin mRNA was 14% in well-differentiated carcinomas, higher than that in poorlydifferentiated carcinomas (86%). A significant correlation was not shown between α-catenin expression and bothdepth of invasion and lymph node metastasis. Moreover, there was no statistical difference between loss or down-regulation of α-catenin mRNA and Helicobacter pylori ( H pylori) infection.CONCLUSION: Downregulation of α-catenin expressionis common in gastric carcinoma, and α-catenin expression may be used as a differentiation marker. Downregulation of α-catenin expression may be an early event in tumorigenesis. Reduced α-catenin expression is not correlated with H pylori infection.