OBJECTIVE: Basic fibroblast growth factor (bFGF) stimulates vascular smooth muscle cell (SMC) migration. We determined whether bFGF increases SMC reactive oxygen-species (ROS) and studied the role of ROS for SMC migration. METHODS AND RESULTS: bFGF rapidly increased rat SMC ROS formation and migration through pathways sensitive to inhibition of NADPH oxidases, PI3-kinase, protein kinase C, and Rac-1. SiRNA directed against the NADPH oxidase Nox4 impaired basal but not bFGF-induced ROS formation and did not affect migration. In contrast, siRNA against Nox1 blocked the agonist-induced ROS generation as well as the bFGF-induced migration. Agonist-induced migration was also attenuated in SMC derived from Nox1 y/- mice and transduction of Nox1 restored normal migration. Likewise, SMC outgrowth in response to bFGF was attenuated in aortic segments from Nox1 y/- mice as compared with Nox1 y/+ mice. bFGF activated JNK but not Src in a Nox1-dependent manner. Consequently, phosphorylation of the adaptor protein paxillin, which is central for migration and secretion of matrix-metalloproteinases, were dependent on Nox1 as well as JNK but not Src. CONCLUSIONS: These data demonstrate that bFGF activates the Nox1-containing NADPH oxidase and that bFGF through a pathway involving ROS and JNK stimulates SMC migration.