SU5416 (Semaxanib) is a potent and selective vascular endothelial growth factor (VEGF) receptor protein tyrosine kinase 1/2 inhibitor that also inhibits other tyrosine kinases KIT, MET, FLT3 and RET. SU5416 inhibited cell migration of human vascular endothelial cells expressing both Flt-1 and KDR in response to VEGF and also inhibited the cell migration in response to placenta growth factor (PIGF), a specific ligand for Flt-1. Chemotaxis of monocytes expressing only Flt-1 was also inhibited by SU5416 in a dose-dependent manner. Moreover, SU5416 was found to inhibit tyrosine kinase of Flt-1 in response to PIGF in vitro. SU5416 efficiently inhibited Kit activity in vivo when administered on a twice-weekly schedule.