Disturbed function of E-cadherin and/or of one of its anchoring proteins, the catenins, is thought to destabilize E-cadherin-mediated cell-cell adhesion, which may enhance the invasiveness of epithelial cells and thus favor carcinoma progression. Reduced expression of E-cadherin and α-catenin, as well as mutations in the E-cadherin gene, have been found in various carcinomas, whereas mutations in the α- and β-catenin genes have been described only in carcinoma cell lines. Using reverse transcription-PCR, followed by agarose gel electrophoresis and single-strand conformational polymorphism, we examined 16 diffuse- and 5 intestinal-type gastric carcinomas, as well as 9 lobular and 2 ductal breast carcinomas, for mutations of α- and β-catenin cDNA. All of the investigated tumors were analyzed previously for E-cadherin mutations. Comparing tumorous and nontumorous samples, we detected neither deletions nor aberrant single-strand conformational polymorphism patterns. At nucleotide 2220 of the α-catenin gene, we identified one frequent polymorphism. Our findings suggest that, in contrast to E-cadherin, mutations of α- and β-catenin do not contribute to the pathogenesis or the diffuse growth patterns of gastric or breast carcinomas.