Platelet-derived growth factor (PDGF) plays a critical role in the pathogenesis of proliferative diseases. NAD(P)H oxidase (Nox)-derived reactive oxygen species (ROS) are essential for signal transduction by growth factor receptors. Here we investigated the dependence of PDGF-AA-induced ROS production on the cytosolic Nox subunits Rac-1 and p47(phox), and we systematically evaluated the signal relay mechanisms by which the alphaPDGF receptor (alphaPDGFR) induces ROS liberation. Stimulation of the alphaPDGFR led to a time-dependent increase of intracellular ROS levels in fibroblasts. Pharmacological inhibitor experiments and enzyme activity assays disclosed Nox as the source of ROS. alphaPDGFR activation is rapidly followed by the translocation of p47(phox) and Rac-1 from the cytosol to the cell membrane. Experiments performed in p47(phox)(-/-) cells and inhibition of Rac-1 or overexpression of dominant-negative Rac revealed that these Nox subunits are required for PDGF-dependent Nox activation and ROS liberation. To evaluate the signaling pathway mediating PDGF-AA-dependent ROS production, we investigated Ph cells expressing mutant alphaPDGFRs that lack specific binding sites for alphaPDGFR-associated signaling molecules (Src, phosphatidylinositol 3-kinase (PI3K), phospholipase Cgamma, and SHP-2). Lack of PI3K signaling (but not Src, phospholipase Cgamma, or SHP-2) completely abolished PDGF-dependent p47(phox) and Rac-1 translocation, increase of Nox activity, and ROS production. Conversely, a mutant alphaPDGFR able to activate only PI3K was sufficient to mediate these subcellular events. Furthermore, the catalytic PI3K subunit p110alpha (but not p110beta) was identified as the crucial isoform that elicits alphaPDGFR-mediated production of ROS. Finally, bromodeoxyuridine incorporation and chemotaxis assays revealed that the lack of ROS liberation blunted PDGF-AA-dependent chemotaxis but not cell cycle progression. We conclude that PI3K/p110alpha mediates growth factor-dependent ROS production by recruiting p47(phox) and Rac-1 to the cell membrane, thereby assembling the active Nox complex. ROS are required for PDGF-AA-dependent chemotaxis but not proliferation.