The effect of topical administration of phosphodiesterase (PDE) 3 inhibitors on the airway is not clear. In order to examine the usefulness of inhaled PDE3 inhibitors in the treatment of asthma, we investigated the bronchodilator effect of inhaled olprinone, a newly developed PDE3 inhibitor, in nine asthmatic patients. On three separate study days, olprinone, salbutamol, or vehicle was administered in a double-blind and randomized fashion, and pulmonary functions were assessed over 60 min. Significant increases in FEV(1) were observed until 45 min after inhalation of olprinone without adverse cardiovascular effects. Mean maximal increases in FEV(1) were 16.0 +/- 4.0 and 20.5 +/- 4.2% with olprinone and salbutamol, respectively. The bronchodilator effect of olprinone was greater than that of salbutamol in four of the nine patients. These results suggest that the inhaled PDE3 inhibitor has a bronchodilator effect in asthmatic patients.