BACKGROUND: Airway inflammation and hyperresponsiveness are recognized as major characteristics of bronchial asthma. Airway inflammation has usually been assessed by invasive methods, e.g. BAL or bronchial biopsy, but recent studies proposed induced sputum as another reliable and non- invasive tool to investigate airway inflammation in asthmatic patients. Thus, the relationship between airway inflammation assessed by induced sputum and airway hyperresponsiveness was investigated in asthmatic patient. METHOD: Airway responsiveness was determined by the concentration that caused a 20% decrease in FEV1(PC20) after inhaling incremental concentrations of methacholine. The numbers of inflammatory cells and the concentration of eosinophilic cationic protein(ECP) were assessed in induced sputum obtained by inhalation of hypertonic saline(3%). RESULT: We analyzed sputum induced in 15 stable asthmatic patients. 1. The differential cell count(%) of macrophages, neutrophils, eosinophils and lymphocytes in induced sputum were 39.1 +/- 27.0%, 29.6 +/- 21.0%, 28.8 +/- 18.8%, 1.3 +/- 3.1% respectively. 2. The mean value of baseline FEV1 (Predicted) and ECP were 76.3 +/- 30.3% and 1,101 +/- 833 micro gram/L respectively. The geometric mean value of PC20 was 0.56mg/mL. 3. The relationships between the sputum eosinophil and ECP in induced sputum, and between sputum eosinophil and degree of airway responsiveness(PC20) were found be significantly correlated (r=0.81, p<0.05 and r=-0.78, p<0.05, respectively). 4. Sputum neutrophils and PC20 were not correlated to each other (r=0.11, p=0.69) and a significant negative correlation was found between ECP and baseline FEV1(predicted) (r=-0.62, p<0.05). CONCLUSION: The results of this study suggest that an induced sputum via a inhalation of hypertonic saline is useful to determine a patient's status of airway inflammation, and airway inflammation is one of the major causal factors in the development of bronchial hyperresponsiveness in asthmatic patients.