Abstract: A residue obtained by removing reserpine completely from the alkaloid of Hainandao roots and three single fractions—"Hainan No. 9", "Kwangsi No. 6", and "Yunnan 2-22"—have been found to produce remarkable fall of blood pressure following intravenous injection into anesthetized dogs. "Kwangsi No. 6" was effective at a dose of 2—3 mg/kg, all the others at a dose of 1 mg/kg. "Kwangsi No. 6" revealed a stronger adrenolytic action. Five hypertensive dogs which received a daily oral dose 10—30 mg/kg of Hainan alkaloid without reserpine showed remarkable fall of blood pressure. Two of them had sedation, tremors, constriction of pupil and relaxation of nictitating membrane; one had diarrhea. The blood pressure of 3 renal hypertensive dogs also dropped following a daily oral administration of "Hainan No. 9" at a dose of 3—20 mg/kg/day. There appeared no side effects, nor was there any untoward effect on the liver, kidney, heart and blood picture.