The increasing prevalence of allergic rhinitis in many countries is becoming a social problem. It is important to determine whether air pollutants are related to the increase in the prevalence rate of allergic rhinitis or not. In this respect, it is necessary to elucidate whether exposure to air pollutants affects the nasal mucosa and causes nasal mucosal hyperresponsiveness to chemical mediators released by antigen-antibody reactions. A previous study revealed that diesel exhaust particulates are potent in augmenting increases in nasal congestion and nasal secretion induced by histamine (T. Kobayashi and T. Ito, 1995, Fundam. Appl. Toxicol. 27, 195-202). In the present study, using a rhinitis model of guinea pigs, we investigated whether short-term (3-hr) exposure to diesel exhaust induces nasal mucosal hyperresponsiveness to histamine. Guinea pigs of each group were exposed to filtered air or to a low or high concentration of diesel exhaust (1 and 3.2 mg/m3 particulates in diluted diesel exhaust, respectively) for 3 hr. After diesel exhaust exposure, sneezing frequency, nasal secretion from the nostril, and intranasal airway resistance induced by histamine were measured as indices of sneezing response, rhinorrhea, and nasal congestion, respectively. Short-term exposure to a low or high concentration of diesel exhaust itself did not induce sneezing, nasal secretion, or nasal congestion. However, short-term exposure to a high concentration of diesel exhaust augmented sneezing and nasal secretion, but not nasal congestion, induced by histamine. In conclusion, short-term exposure to diesel exhaust potently induces nasal mucosal hyperresponsiveness.