The bronchial effect of intravenous atenolol (ICI 66.082) has been studied in a doubleblind cross over trial in 10 patients with pronounced, labile bronchial asthma. A single i. v. dose of atenolol 3 mg, sufficient to cause a fall in heart rate and systolic blood pressure at rest, induced only a slight and clinically almost negligible impairment of ventilatory function. An ordinary therapeutic dose of salbutamol by inhalation far outweighed the bronchial effect of atenolol. The drug appears promising with regard to its cardio-selective properties.