Airway inflammation is a major factor in the pathogenesis of asthma. Inducing sputum by hypertonic saline is a noninvasive method of assessment of the airway inflammation in asthmatic patients. To investigate sputum induction as a method for assessing airway inflammation and to evaluate the effect of inhaled beclomethasone dipropionate (BDP) in asthmatic patients, we examined the bronchial hyperresponsibility (BHR), pulmonary function and differential cell counts in induced sputum of the patients before and after BDP therapy. In asthmatic patients, the percentage of eosinophils in induced sputum was significantly higher than that in non-asthmatic subjects. Ten patients with atopic asthma (four men and six women; mean [+/- SD] age, 30.5 +/- 12.4 years) participated. Their mean percentage of eosinophils (% eosinophils) in induced sputum fell from 22.9 +/- 7.2% to 13.9 +/- 8.3% (p < 0.05) by 3 months of BDP treatment. The percentage of eosinophils in induced sputum before BDP treatment was significantly correlated with the ratio of the forced expiratory volume in one second to the forced vital capacity (FEV1%) at baseline (r = -0.75, p < 0.05), but not with log Dmin at baseline (p = 0.18). The change in FEV1% between at baseline and post-treatment correlated significantly with the change in the sputum eosinophil percentage (r = -0.79, p < 0.01). In addition, there was a significant correlation between the change of log Dmin and the change of the sputum eosinophil percentage (r = -0.64, p < 0.05). In conclusion, analysis of induced sputum is a safe, noninvasive, repeatable and useful method to assess the clinical condition of bronchial inflammation in patients with bronchial asthma.