A number of studies have shown short term hemodynamic and symptomatic improvement in patients with essential hypertension under treatment with diltiazem. The long-term efficacy of the oral calcium antagonist, diltiazem, remain to be established in patient studies. We evaluated this drug in 70 patients with WHO classification 1-3 hypertension. Diltiazem was tested alone in 25 patients, in combination with diuretics in 14 patients and other drugs in 31 patients with essential hypertension. The fall in blood pressure after oral diltiazem was maximum with 24 weeks and then the fall continued steadily with significant improvement as judged by subjective patients impression in each group. The efficacy ratio of diltiazem was 57.1% in remarkably effective cases, 22.9% in effective, 10% in moderately effective and 10% in not effective cases. And this efficacy ratio was most prominent in other drugs concomitant group, followed by the diltiazem monotherapy group and in the diuretic concomitant use group. We concluded the oral calcium antagonist, diltiazem, is effective in patients with essential hypertension, providing significant blood pressure and symptomatic benefit with long-term treatment.