The effects of three beta-adrenergic stimulating agents, isoproterenol, salbutamol, and terbutaline, were studied in the cat. In animals receiving halopropane, the dose of salbutamol or terbutaline necessary to produce ventricular arrhythmias was 100-500 times greater than the dose of isoproterenol needed. In cats receiving nitrous oxide, a dose of carbachol which increased airway pressure 50-135 per cent for a preset tidal volume was given. This action of carbachol was blocked by 2 µg/kg of salbutamol or terbutaline. The large differences between bronchodilating and arrhythmia-producing doses of salbutamol and terbutaline suggest that these agents might be of value in the treatment of bronchoconstriction in conscious and anesthetized patients.