Thirty-one patients with a dry cough for at least 1 h duration in more than half of the last 30 days and with no recent respiratory infection participated in a clinical trial to evaluate the effect of inhaled beclomethasone dipropionate (BDP). Lung function was normal and reversibility was excluded by spirometry before and after bronchodilator and by no diurnal variation in home peak flow monitoring. Only one had significant eosinophilia and only three were mildly hyperreactive by bronchial provocation with histamine. After a 1-week run-in period the patients were randomly allocated to receive either BDP 4 puffs of 50 micrograms b.i.d., or placebo. After 2 weeks the patients were crossed over and received the alternative treatment for another 2-week period. The degree of cough, disturbance of night sleep and peak expiratory flow morning and evening were recorded daily in a diary. Spirometry was performed at each control visit. A significant period effect from run-in to period 1 and/or from period 1 to period 2 was demonstrated for cough and disturbance at night but not for peak flow or spirometry. However, no significant treatment effect was found for any of the measured variables.