Inhalation of medication is the preferred method for treating reversible airway obstruction; however, difficulties in the use of pressurized canisters frequently lead to suboptimal results. The Aerochamber (Monoghan Medical Corp) is a portable breath-actuated device that attaches to a metered-dose inhaler (MDI) and is designed to overcome many of the problems of aerosol delivery encountered by some patients. The attachment of this breath-actuated device to an MDI reduced pharyngeal deposition of aerosol 14-fold, but delivery of aerosol to intrapulmonary airways in normal subjects and patients with bronchitis remained unchanged. In a group of nine patients with stable asthma, inhalation of a bronchodilator aerosol using the breath-actuated device (Aerochamber) achieved effective bronchodilation similar to an optimally administered MDI. Advantages of the breath-actuated device (Aerochamber) include (1) aerosol delivery of medication whether or not the discharge of aerosol is synchronized with inhalation, (2) effective therapeutic response compared with optimally administered MDI; (3) greatly reduced deposition of aerosol in the upper airways, which might be expected to reduce adverse effects of steroids; and (4) universal application to all bronchodilator and steroid MDIs.