Cell-cell adhesion is mediated by cadherins (integral membrane proteins) which form a complex with catenins (cytoplasmatic proteins). Down-regulation of cadherins and more recently of catenins has frequently been detected in many types of human carcinomas, in which it has been associated to tumor progression. While E-cadherin expression has been extensively studied in many forms of human cancers, including oral SCC, less is known about the expression levels of catenins in oral SCCs. The objective of this study was to evaluate the role of these proteins in the carcinogenetic process of the oral cavity. We evaluated by immunohistochemistry beta- and gamma-catenin expression in 30 cases of intraoral squamous cell carcinomas at different degree of cellular differentiation. As already reported for E-cadherin, the beta- and gamma-catenin expression showed an inverse relationship with the degree of differentiation, being the membranous expression of both catenins homogeneously reduced in less differentiated oral squamous cell carcinomas (grade 3). More interestingly, a decreased expression of these molecules was also found at the invasive front of grade 2 and sometimes of grade 1 carcinomas, thus suggesting a more aggressive biological behavior of these cancer cells. An absent staining for both beta- and gamma-catenins could constitute a hallmark of aggressive biological behavior even in tumor still well or moderately differentiated, at least in the peripheral invading front constituted by less differentiated tumor cells.