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To gain further insight into the kinetics of airway inflammatory response and explore the possibility of nitric oxide as a surrogate marker of the lower airway inflammatory response to ozone, nine subjects with mild atopic asthma were exposed to filtered air or 0.2 ppm ozone for 2 hours with intermittent exercise. Lung function was measured at baseline and immediately after exposures. Sputum induction was performed at 6 hours and at 24 hours after exposures, and exhaled nitric oxide levels were measured at baseline, immediately, 6, and 24 hours after both exposures. A significant decline in forced expiratory volume in one second and inspiratory capacity was detectable following exposure to ozone. In addition, a 2-fold increase was observed in the percentage of polymorphonuclear leukocytes 6 hours after exposure to ozone, with no changes in other biomarkers at this time point. By 24 hours after ozone exposure, the neutrophilia had subsided but there was an increase in albumin, total protein, myeloperoxidase, and eosinophil cationic protein. Exhaled nitric oxide levels, histamine, interleukin-8, and growth-related oncogene-alpha in sputum did not change significantly following ozone exposure. It was concluded that short-term ozone exposure induces an acute inflammatory response in asthmatic airways, characterized by early polymorphonuclear leukocyte influx followed by plasma extravasation and activation of eosinophils and neutrophils. Exhaled nitric oxide is not a useful marker for detecting inflammatory response to ozone in persons with mild asthma.