Eph receptors are the largest known family of receptor tyrosine kinases. The Eph receptors and their membrane-attached ligands,the ephrins,show diverse expression patterns during development.Functional studies have demonstrated that Eph receptors and ephrins play important roles in many developmental processes including formation of neuronal network,patterning of neural tube and paraxial mesoderm, guidance of cell migration and axon pathfinding,and vascular formation.Recent studies have also suggested that Eph receptors and ephrins may be involved in carcinogenesis.It is therefore of clinical importance to further analyze the function of these molecules,particularly their function in tumor cell growth,since manipulation of the activities of these molecules may have therapeutic applications.