Fifteen adult asthmatics participated in a controlled open randomized study to compare the efficacy on exercise-induced asthma of pretreatment with 1 mg fenoterol administered as inhalation powder and from a pressurized aerosol. Both types of treatment were inhalations of 5 single doses of 0.2 mg fenoterol over a period of 10 minutes. A run of 6 minutes was carried out on a treadmill in a climate chamber 30 minutes after the beginning of the pretreatment, at the same time of day on three days. After pretreatment with the pressurized aerosol a fall was seen in peak expiratory flow of 28% (+/- 5%, SEM) and after pretreatment with inhalation powder the fall was 18% (+/- 4%). This is a statistically significant difference (p less than 0.01).