Eosinophilic bronchitis presents with chronic cough and sputum eosinophilia, but without the abnormalities of airway function seen in asthma. It is important to know how commonly eosinophilic bronchitis causes cough, since in contrast to cough in patients without sputum eosinophilia, the cough responds to inhaled corticosteroids. We investigated patients referred over a 2-yr period with chronic cough, using a well-established protocol with the addition of induced sputum in selected cases. Eosinophilic bronchitis was diagnosed if patients had no symptoms suggesting variable airflow obstruction, and had normal spirometric values, normal peak expiratory flow variability, no airway hyperresponsiveness (provocative concentration of methacholine producing a 20% decrease in FEV(1) ([PC(20)] > 8 mg/ml), and sputum eosinophilia (> 3%). Ninety-one patients with chronic cough were identified among 856 referrals. The primary diagnosis was eosinophilic bronchitis in 12 patients, rhinitis in 20, asthma in 16, post-viral-infection status in 12, and gastroesophageal reflux in seven. In a further 18 patients a diagnosis was established. The cause of chronic cough remained unexplained in six patients. In all 12 patients with eosinophilic bronchitis, the cough improved after treatment with inhaled budesonide 400 micrograms twice daily, and in eight of these patients who had a follow-up sputum analysis, the eosinophil count decreased significantly, from 16.8% to 1.6%. We conclude that eosinophilic bronchitis is a common cause of chronic cough, and that sputum induction is important in the investigation of cough.