Oxitropium bromide (Ba 253) is a new inhaled bronchodilating agent with anticholinergic properties. The effect of this compound (100 μg) was compared to that of ipratropium bromide (40 μg), the β2-receptor stimulant fenoterol (400 μg) and placebo in 8 patients with exercise-induced asthma. The drugs were administered by metered dose inhalers, after which exercise tests were performed on ergometer cycles at the times of the drugs’ maximal effects. Forced expiratory volume during 1 s and vital capacity were recorded basally, repeatedly during 20 min after exercise and following the inhalation of isoprenaline (160 μg) which was given 20 min after exercise. Fenoterol possessed a very good protective effect against exercise-induced bronchoconstriction in all patients, whereas the other drugs differed very little from placebo. Thus, only 4 patients did benefit from ipratropium bromide, 1 patient from oxitropium bromide and 2 patients from placebo. No side effect occurred. In the doses used the two anticholinergic agents ipratropium bromide and oxitropium bromide were less effective than a β2-adrenoreceptor stimulant like fenoterol in protecting against exercise-induced