Receptors of the integrin family regulate adhesion and terminal differentiation of keratinocytes. In order to investigate the significance of changes in integrin expression associated with malignant transformation we have examined normal human oral keratinocytes and seven oral squamous cell carcinoma (SCC) lines. Cell surface levels of the alpha 2, alpha 3, alpha 5, alpha 6, alpha v, beta 1 and beta 4 integrin subunits were determined by flow cytometry and the distribution of the beta 1 subunit was examined by immunohistochemistry. In normal keratinocytes and one SCC line the beta 1 subunit was most abundant in the basal cell layer, but in other lines anti-beta 1 antibodies stained basal and suprabasal layers uniformly. All lines had reduced surface levels of at least one integrin subunit and in some cell lines distinct subpopulations could be distinguished on the basis of differences in integrin expression. Reduced integrin expression was not, however, generally reflected in reduced adhesion to laminin, fibronectin, type IV collagen or vitronectin in three cell lines examined. Those cell lines with the lowest capacity for terminal differentiation, as measured by involucrin expression, had the lowest levels of the alpha 6 and beta 4 subunits or were completely lacking alpha v. Oral SCC show considerable variation in integrin expression, but focal or extensive loss of the alpha 6 and beta 4 subunits is a common feature of poorly differentiated tumours. The cell lines we have examined therefore provide a relevant experimental model with which to explore the relationship between aberrant integrin expression and impaired terminal differentiation capacity.