Propranolol (Inderal) is safely compatible with a light plane of halothane anaesthesia in an atropinized patient with a normal cardiovascular system. It prevents the cardiac overactivity and the arrhythmias caused by fear, pain, vagolytic drugs, surgical stimulation and catecholamines. Judging from its effects on the volume-pulse wave, the electrocardiogram, the systolic blood pressure and the pulse-wave velocity, it has been concluded that the combined effects of light halothane anaesthesia and beta-adrenergic blockade with propranolol do not appreciably impair the intrinsic contractility of the healthy myocardium or its ability to respond immediately to an increase in the venous return in atropinized vasodilated patients. The potential risks of beta-adrenergic blockade in anaesthetics have been discussed. The results of this investigation are not applicable to any anaesthetic agent other than halothane.