Hypertonic saline aerosols are being used increasingly for bronchial provocation testing and induction of sputum. The aims of this study were to assess the response to challenge with 3% hypertonic saline administered via a ultrasonic nebulizer in patients with asthma, and to evaluate relationship between % fall of FEV₁ during induction of sputum (osmotic airway hyperresponsiveness; osmotic AHR) and biochemical markers of induced sputum. We investigated changes in FEV₁ in response to inhaling ultrasonically nebulized 3% saline in 25 patients with asthma and 10 control subjects. FEV₁ was measured before, during, and after induction of sputum. We used fluoroimmunoassay to detect eosinophil cationic protein (ECP), immunohistochemical staining to detect EG2+ (secretory form of ECP) eosinophils, and a sandwich ELISA to detect interleukin (IL)-5. Protein concentration was determined by using bicinchoninic acid protein assay reagent. Asthmatics, compared with controls, had significantly higher osmotic AHR. Moderate to severe asthmatics had significantly higher osmotic AHR compared to mild asthmatics. Osmotic AHR was significantly correlated with the proportion of eosinophils, the levels of ECP, EG2+ eosinophils, IL-5, and proteins. These data suggest that osmotic AHR is closely related to the clinical status and biochemical markers of sputum supernatant in asthmatic patients.