BACKGROUND: Chronic cough, defined as a cough persisting for three weeks or longer, Is a common symptom for which outpatient care is sought. The most common etiologies of chronic cough are postnasal drip, asthma, arid gastroesophageal reflux. Methacholine challenge is a useful diagnostic study in the evaulation of chronic cough, particularly useful in chronic cough patients with asthmatic symptom. Patients with chronic cough may have dysfunction of bronchial and extrathoracic airways. To evaluate if dysfunction of the bronchial and extrathoracic airways causes chronic cough, we assessed bronchial (BHR) and extrathoracic airway (EAHR) responsiveness to inhaled methacholine in patients with chronic cough. METHODS: 111patients with chronic cough were enrolled in our study. Enrolled patients had no recorded diagnosis of asthma bronchopulmonary disease, hypertension, heart disease or systemic disease and no current treatment with bronchodilator or corticosteroid. Enrolled patients consisted of 46 patients with cough alone, 24 patieots with wheeze 22 patients with dyspnea; 19 patients with wheeze and dyspnea. The inhaled methacholine concentrations causing a 20% fall in forced expiratory volume in 1 s (PC20FEV1,) and 25% fall in n axiital midinspiratory flow (PC25MIF50) were used as bronchial and extrathoracic hyperrespornsiveness. RESULTS: There were four response patterns to methacholine challenge study HEIR in 27 patients, EAHR in 16 patients, combined BHR and EAHR in S patients, and no hyperresponsiveness in 60 patients. In patients with cough alone, there were BHR in 3 patients, EAHR in 9 patients, and combined BI-IR and EAHR in 2 patients. In patients with wheeze and/or dyspnea, there were BHR in 24 patients, EAHR in 7 patients, and BHR and EAHR in 6 patients. Compared with patients with wheeze and/or dyspnea, patients with cough alone had more common EAHR than BHR. In patients with wheeze mad/or dyspnea, BHR was more common than EAHR. CONCLUSION: These results show tint among patients with hyperresponsiveness to methacholine, those with dyspnea and/or wheezing had mainly bronchial hyperresponsiveness, whereas those with chronic cough alone had mainly extrathoracic airway hyperresponsiveness.