Formoterol administered by a dry-powder (DP) capsule inhaler was compared with a pressurized metered-dose inhaler (pMDI) with regard to bronchodilating and systemic effects. The study used a double-blind, crossover, double-dummy technique. Twelve patients with moderate reversible asthma in a stable phase were examined on two separate study days, and the inhalers were given in randomized order. After baseline measurements, increasing doses of formoterol were given at intervals of 75 min. FEV1 and heart rate and tremor measurements were repeated after each dose, and the doses were 12 + 12 + 24 + 48 micrograms, giving a total dose of 96 micrograms. The peak expiratory flow rate (PEFR) was recorded in the morning before the first dose, after the last dose, and then repeatedly at home until 19 h after the last dose. There was an equal increase in ventilatory capacity at each dose level, independent of inhaler device. Repeated PEFR measurements after the last dose did not reveal any differences in duration of effect. There was a slight but statistically significant increase in heart rate and tremor after the highest doses of the DP formulation compared to the pMDI. These systemic effects can probably be explained by the reduced oral deposition of the aerosol caused by using a spacer. This study indicates that the DP and pMDI formulations of formoterol are equipotent in bronchodilation.