The bronchodilating activity and tolerability of a single 0.5-mg oral dose of broxaterol (Z.1170) were evaluated in 18 patients with reversible bronchial obstruction. Salbutamol 4.0 mg and placebo were used as controls. The study design was double-blind within patients. The forced expiratory volume in 1 s (FEV₁), pulse rate, and blood pressure were measured immediately before and 0.5, 1, 2, 3,4, 5, and 6 h after each treatment. At the same time clinical controls were made to detect the possible presence of side effects. Both broxaterol and salbutamol caused significant increases in FEV₁ until the 5th hour as compared to baseline values and until the 2nd hour as compared to placebo. No significant difference was reported between the effects of broxaterol and those of salbutamol at all the times considered. The tolerability of broxaterol was good, as was that of salbutamol. The pulse rate and blood pressure did not show any significant clinical variations. The side effect reported most frequently was tremor.