The purpose of this study was to observe the additive effect of halothane anesthesia and propranolol, and also the effect of atropine and isoproterenol on the heart rate and the blood pressure after propranolol during halothane anesthesia in human-volunteers. The results were as follows: 1) In conscious patients, 10 minutes after intravenous administration of 1.0mg propranolol the heart rate was slower but there was no significant change in the blood pressure. 2) Twenty-thirty minutes after halothane anesthesia, the heart rate was slower by 6 to 8 beats per minute: systolic and diastolic blood pressure was lower by 20.4 torr and 10.5 torr, respectively. 3) 10 minutes after intravenous administration of 1.0mg propranolol during halothane anesthesia, the heart rate was decreased by 7.8, 7.0 per minute: systolic and diastolic blood pressure decreased by 6.7, 5.7 torr and 3.0, 3.9 torr in the atropine and isoproterenol group, respectively. 4) One minute after intravenous administration of atropine 0.5mg after propranolol 1.0mg during halothane anesthesia, the heart rate increased by 12.1 per minute and persisted so far 10 minutes, but the blood pressure did not increase. 5) One minute after intravenous administration of isoproterenol 0.025mg after propranolol 1.0mg during halothane anesthesia, the heart rate had markedly increased by 35, but normalized 10 minutes later. The systolic blood pressure was increased by 13.4 torr but normalized 10 minutes later. 6) The above results indicate: Atropine increases the heart rate which has been slowed with propranolol during halothane anesthesia: isoproterenol increases the heart rate and blood pressure but the duration of action was short. Therefore, authors considered that atropine is useful for the maintenance of heart rate, and continuous administration of isoproterenol for maintenance of blood pressure and heart rate after propranolol during halothane anesthesia.