The introduction of induced sputum, as the diagnostic and research tool allowed to define nonasthmatic eosinophilic bronchitis characterized as a chronic cough in patients with no symptoms or objective evidence of variable airflow obstruction, with normal airway hyperresponsiveness and sputum eosinophilia. Eosinophilic bronchitis is an important cause of chronic cough. Studies in which the assessment of airway inflammation has been undertaken in chronic cough patients have shown that nonasthmatic eosinophilic bronchitis accounts for 10 to 30% of cases referred for specialist investigation. Eosinophilic bronchitis, like asthma, is characterized by eosinophilic airway inflammation, but unlike asthma, there is no airway hyperresponsiveness or bronchoconstriction. The airway immunopathology of asthma and eosinophilic bronchitis are almost identical. An obvious question is why an apparently similar pattern of airway inflammation is associated with different functional abnormalities in patients with nonasthmatic eosinophilic bronchitis and asthma. The differences in functional association may be related to differences in the localization of mast cells within the airway wall, with airway smooth muscle infiltration occurring in patients with asthma, and epithelial infiltration in patients with nonasthmatic eosinophilic bronchitis.