FeNO is produced by inducible nitric oxide synthase in the bronchial epithelia constituting the mucous membranes of the airway.33 The measurement of FeNO concentrations is used as a method of assessing airway inflammation.34,35 In previous studies, it has been reported that increases in FeNO concentrations are associated with exposure to air pollution.8 In the present study, FeNO concentrations increased significantly with increased O3 and SPM concentrations only among subjects with a history of asthma, despite the limited number of subjects with such a history. The gene discussed is NOS2; the disease is asthma.