Abstract: Corydalis B (dl-tetrahydropalmatine) and L, isolated from Corydalis ambigua Cham. et Sch. by Prof. T. Q. Chou, were found to possess marked analgesic activity and less tolerance than morphine. In the present work their effects on blood pressure, cardiac rhythm and respiration were studied. The blood pressure of the carotid artery was recorded and EKG of lead Ⅱ was taken in anesthetized cats. The respiratory minute volume was measured in unanesthetized rabbits. The results were as follows: Corydalis B 40 mg/kg (approximately twice the analgesic dosage) produced bradycardia and a gradual decrease of blood pressure by 20--40 mm Hg which slowly recovered within 1 hour. There was no significant change in EKG. Intravenous injection of 60 mg/kg gave a temporary increase of respiratory minute volume by 130--165 ml (26--37% above the original level) for 1--2 minutes and then a decrease of 85—320 ml/min (20--48% bolow the original level). The respiratory volume gradually returned to the original level in 1/2-1 hour. The respiratory rate showed little change. Corydalis L 30 mg/kg (approximately twice the analgesic dosage) rendered a lowering of blood pressure by 30--60 mm Hg within 5--10 minutes, accompanied by bradycardia and inverted T-wave. Respiratory minute volume gradually increased by 170—300 ml (30—60% above the original level) for 1--1 1/2 hours, but the respiratory rate showed no significant change.