All the consecutive patients who presented with CC as their main symptom in the period between January 2002 and June 2008 and had normal spirometric and chest radiographic results were enrolled in the study. The exclusion criteria were as follows: severe systemic illnesses; known bronchopulmonary diseases; acute respiratory tract infections in the last 2 months; treatment with H1- and H2-antihistaminic, antitussive drugs, bronchodilators, oral corticosteroids, or ICSs in the last month, and current treatment with angiotensin-converting enzyme inhibitors and β-blockers. A total of 372 patients were enrolled in the study. Fifty-two steroid-naive patients with mild persistent asthma and normal spirometric results receiving diagnoses in the same period who did not complain of cough (asthma/CC− patients) served as control subjects.