BACKGROUND AND OBJECTIVES: We performed this study to compare the endothelial function of the patients with newly diagnosed essential hypertension(EH) to age and sex-matched normal subjects or patients with known coronary artery disease(CAD) and to evaluate the effect of calcium channel blockers(amlodipine) on the endothelial dysfunction in patients with EH. MATERIALS AND METHOD: The endothelial function, expressed as percent brachial artery diameter changes at hyperemic phase compared to resting state, using high-resolution ultrasound was measured before taking amlodipine and 3 to 4 months after taking amlodipine(5 to 10 mg daily), when the high blood pressure(BP) was well controlled(129/83 mmHg), in patients with EH(mean age; 53 yrs, n=2). We also measured the endothelial function in normal subjects(mean age; 54 yrs, n=5) and patients with proven CAD(mean age; 56 yrs, n=0). RESULTS: The mean BP of the patients with EH, CAD, and normal subjects were 172/108 mmHg, 110/69 mmHg, and 113/72 mmHg, respectively. There were no significant differences among the study groups in regard to the serum glucose and various lipid levels. The endothelial function of the patients with EH(6.6+/-2.3%) was significantly(p=.000) lowered when compared to the normal subjects(14.3+/-3.3%), but did not show any significant differences when compared to the patients with CAD(8.6+/-3.4%). The endothelial function in patients with EH was significantly(p=.007) improved from 6.6+/-2.3 % to 11.0+/-2.7 % 3 to 4 months after taking the amlodipine. CONCLUSION: Calcium channel blockers, especially amlodipine, can improve endothelial dysfunction in patients with EH as well as controlling high BP.