Eighteen adult asthmatics participated in a placebo controlled, double-blind, randomised study comparing the efficacy of pretreatment with fenoterol administered by pressurized aerosol and as a dry powder on exercise-induced asthma. The dosages used were 0.6 mg and 1.0 mg as both pressurized aerosol and dry powder. The pretreatment was given over a period of 10 min. Six min of treadmill-running was performed in a climate chamber 30 min after pretreatment on five successive days. The lung function was assessed by peak expiratory rate. The decrease in lung function following pretreatment with placebo was 32% (average +/- (SEM) (2). Falls of 9% (2) and 8% (1) were seen after pretreatment with 0.6 and 1.0 mg from a pressurized aerosol. The falls following pretreatment with 0.6 and 1.0 mg of dry powder were 8% (2) and 8%, respectively. It is concluded that pretreatment of exercise-induced asthma with a beta-2-agonist is equally effective whether dosed from a pressurized aerosol as when given as a dry powder. A dose of 0.6 mg is just as effective as a dose of 1.0 mg when inhaled over a period of ten min.