In order to determine the bronchodilating activity and safety of two beta-2-receptor agonists, broxaterol and procaterol, compared with a placebo, 12 patients with reversible airway obstruction were tested in a double-blind cross-over study. The drugs were administered orally and the dosage of broxaterol was 0.5 mg, that of procaterol 0.05 mg. Measurements of forced expiratory volume in 1 s (FEV1), heart rate and blood pressure were performed before and 30, 60, 120, 240, 360, and 480 min after each treatment. Both drugs produced bronchodilation but broxaterol was statistically 30 min faster in producing this effect than procaterol (p less than 0.05). Moreover this effect for both drugs persisted significantly for up to 480 min compared with the effect of the placebo (p less than 0.005). There were no significant side effects with either drug. Heart rate and blood pressure did not show any changes in clinical significance for broxaterol or procaterol. In our study, broxaterol showed a faster bronchodilating effect than procaterol, and tolerance was the same for both drugs.