Abstract-Oxidative stress contributes to the pathogenesis of atherosclerosis. p22phox -based NAD(P)H oxidases exist in the vessel wall, acting as important superoxide-generating systems in the vasculature. Some studies have identified reduced atherosclerosis in the presence of the C242T CYBA polymorphism, whereas others have not. Because vascular p22 phox is identical to neutrophil p22 phox , we studied the association between the C242T, A640G, and Ϫ930 A/G CYBA polymorphisms and the quantity of superoxide produced from neutrophils isolated from healthy adults to determine if these polymorphisms had any functional impact on NADPH oxidase function. Neutrophils were isolated from 90 subjects by Percoll density gradient centrifugation. Genotypes were determined by polymerase chain reaction (PCR) and restriction mapping, as well as real-time PCR. The oxidative burst was stimulated with phorbol 12-myristate 13-acetate. Superoxide was quantified using the superoxide dismutase inhibitable oxidation of the spin probe hydroxylamine 1-hydroxy-3-carboxy-pyrrolidine, detected by electron paramagnetic resonance. Superoxide production was significantly affected by the C242T polymorphism, being 8.7Ϯ0.7, 7.9Ϯ0.6, and 5.9Ϯ1.2 mol/L per minute per 10 6 neutrophils for the C242T CC, CT, and TT genotypes, respectively (PϽ0.05). In contrast, the A640G and the Ϫ930