The hypotensive action of calcium antagonist has been recognized, however, clinical study on the hypotensive effect is not yet extensively carried out. Auther studied the effect of Dilitiazem(Herben(R)) on 23 hypertensive patients. The age of patient was average 58.5(30-75) years. There were 8 male and 15 female patients. Among 23 cases, 20 cases of essential hypertension had no previous medication for hypertension and they were given 90mg of Diltiazem daily in 3 divied doses for 8 weeks. The blood pressure and pulse were measured at one week interval. In 3 cases of hypertension who were refractory to other hypotensive drugs for 2 weeks. The results were as follows; 1) In 20 cases of untreated essential hypertension, the control average blood pressure was 179.8/106.3mmHg and pulse 77.1/min. After the Diltiazem medication average blood pressure in one week was 153.3/97.3mmHg and pulse 76.6/min, in 3 week 153.0/94.0mmHg, and pulse 76.6/min, in 5 week 143.0/92.0mmHg and pulse 75.4/min, and in 8 week 142.3/90.0mmHg and pulse 73.0/min. These data showed that after one week of medication, blood pressure fell significantly in systole and diastole but there was no significant pulse change. 2) The rate of hypotensive effect by grade were as follows; overall effectiveness in systolic pressure which fell more than 5 mmHg was 85% and more than 20mmHg fall was 70%. In diastolic pressure the overall effectiveness which fell more than 5mmHg was 60% and more than 15 mmhg fall was 40%. 3) In 3 cases which were refractory to other hypotensive drugs, the hypertension became normal blood pressure in one day by 90mg Diltiazem and the fall of blood pressure persisted for 2 weeks by continuous medication.