Forty-three patients with obstructive airways disease took part in three studies designed to determine the importance of three modes of inhalation of a beta 2-agonist on bronchodilator response. Under the conditions of the test, lung volume at the time of aerosol release and the time interval between the 2 puffs had no significant effect upon bronchodilator response, but a fast inspiratory flow rate was found to be associated with a significant reduction in response.