Focal adhesion kinase (pp125FAK or FAK) is a protein tyrosine kinase which is associated with intracellular signalling cascades which are initiated when the integrin family of cell adhesion molecules engage extracellular matrix molecules. In cultured cells, this molecule is physically associated with focal adhesions, which are well-defined regions of intimate cell-to-substratum adhesion. In this location, it interacts with other proteins of the focal adhesion to activate intracellular signalling events associated with cell adhesion. The in vitro expression of FAK and its level of phosphorylation appear to be related to several physiological phenomena, including cell spreading, cell differentiation, cell locomotion and cell death. Because these phenomena are all of critical importance during morphogenesis, and because FAK is expressed in embryonic cells, evidence has been accumulating to indicate that FAK may be an important modulator of developmental processes. In this review, this evidence is surveyed together with evidence from analogous situations, such as tumour cell migration and invasiveness. Although evidence suggesting a role for FAK in morphogenesis is accumulating, current uncertainties regarding its cytoplasmic location and its molecular interactions in vivo make it difficult to reach definitive conclusions regarding the significance of its contributions to developmental processes.