OBJECTIVE The purpose of this study was to examine the effects of NO(2), a major component of air pollution, on airway eosinophilic inflammation and bronchial hyperreactivity, using a mouse model of asthma. METHODS BALB/c mice (eight mice per experimental group) were studied in a basic research laboratory at the University of Iowa. METHODS Using a standard murine model of asthma, BALB/c mice were sensitized to ovalbumin (OVA) by intraperitoneal (IP) injections (days 1 and 7) and were challenged with aerosolized OVA (days 13 and 14). Some mice were exposed to NO(2) (2 ppm) in an exposure chamber for 24 h before undergoing OVA aerosol challenge. A control group was exposed to OVA alone. RESULTS The outcomes assessed included airway inflammation, bronchial hyperreactivity to inhaled methacholine, and goblet cell hyperplasia. We found that NO(2) exposure modestly increased airway neutrophilia but not airway eosinophilia in OVA-exposed mice. These mice exhibited epithelial damage and loss of epithelial mucin. Surprisingly, nonspecific bronchial hyperreactivity (ie, enhanced pause index) was not increased, although baseline smooth muscle tone was increased (p < 0.05) in the mice exposed to NO(2). CONCLUSIONS These data indicate that relatively short-term (24 h) exposure to NO(2) causes epithelial damage, reduced mucin expression, and increased tone of respiratory smooth muscle. Reduced mucin production may be a mechanism of injury following long-term exposure to inhaled NO(2). Despite enhancing epithelial damage in OVA-exposed mice, NO(2) exposure does not otherwise alter the expression of allergen-induced airway responses.