In a double-blind, crossover study, nebulized ketanserin, a 5-HT2 receptor antagonist, and a placebo were given to eight patients with moderate to severe nonasthmatic COPD. Intravenous ketanserin had rapid onset of action and induced a longer lasting bronchial response than inhaled ketanserin. These results confirm that ketanserin acts as a mild bronchodilator in patients with COPD and demonstrate that the inhaled route has no advantage over the intravenous route in terms of effectiveness. Thus, 5-HT may play a role in bronchomotor tone, at least in patients with chronic airway obstruction.