Cell-matrix interaction is crucial in regulating osteoblast differentiation and function. These interactions are themselves regulated, at least in part, by integrins. Although there are some data from mammalian models, few studies have compared integrin expression at different stages of the osteoblast lineage. Here, primary human mandibular osteoblast cultures were grown in the presence of epidermal growth factor (EGF), giving a proliferative, less differentiated phenotype, or of vitamin D-3 and hydrocortisone (D + He), giving a more differentiated phenotype. These cultures were compared with those of cells prepared in the absence of EGF or D + He by fluorescence-activated cell sorter using a panel of monoclonal antibodies to specific integrin heterodimers. To provide in vivo correlation, the same panel of antibodies was used to stain fresh-frozen, undemineralised sections of human mandibular bone. Under baseline conditions the alpha (3), alpha (5), alpha (v) alpha (v)beta (3), beta (3) and beta (1) integrin subunits were expressed strongly by the cells, with low-level expression of the alpha (1), alpha (2) and alpha (4) subunits. In the presence of EGF there was increased a, expression. With D + He, alpha (3) and alpha (5) expression was elevated. Immunohistochemical analysis demonstrated alpha (2), alpha (3), alpha (5), alpha (v)beta (3), beta (1) and beta (3) subunits in cells of the osteoblast lineage; alpha (2) staining was restricted to cells close to the bone surface whilst alpha (v)beta (3) and beta (3) were most frequently localised in the osteocytes. The results proc ide evidence that cells at successive stages of the osteoblast lineage show different patterns of integrin expression. These integrins may be important in cell-matrix interactions leading to osteoblast differentiation.