The cardiorespiratory effects of intravenous infusions of isoprenaline and salbutamol (1 and 5 mug/min) have been compared in twelve dogs.2. Both drugs produced a rise in pulse rate, a fall in systemic arterial pressure and a rise in pulmonary arterial pressure. Salbutamol produced a greater increase in cardiac output than isoprenaline.3. Both drugs produced an increase in venous admixture, but a significant fall in arterial oxygen tension occurred only with isoprenaline at the higher dose.