In this study. the effect of the herbal prescription Tian Ma Gou Teng Yen (TGY), which is traditionally used to treat certain diseases associated with elevated arterial pressure (AP), on the general development of hypertension was investigated in the spontaneously hypertensive rat (SHR). An aqueous extract of TGY was given orally (0.5 ml/100g body weight) to 5 week old SHR twice a day for six consecutive days followed by one day without herbal therapy. The herbal prescription was administered until the SHR were 16 weeks of age. Admininstration of TGY significantly altered the development and prevented hypertension in SHR. On the other hand, heart rat, body weight, food and water intake, and urine volume and electrolytes were not altered. These data suggest that the effect of TGY on AP was through an action of TGY on sympathetic vasomotor activity.