Human deficiency of NADPH oxidase is known as chronic granulomatous disease, and results in chronic recurrent infections, and increased susceptibility to lethal infections as a result of the inability to produce ROS (Good et al., 1968; Dinauer et al., 2000) NADPH oxidase pumps large amounts of superoxide into the phagocytic vacuole, where it is converted to H2O2. The gene discussed is FMO5; the disease is chronic granulomatous disease.