Aim The purpose of this study was to evaluate whether endothelium dependent (nitric oxide mediated) dilation of the brachial artery is impaired in patients with grade 1 and 2 essential hypertension,but no other risk factors and the role of hypertension in endothelial function. Methods We studied 25 patients with hypertension and 25 control subjects. Flow mediated dilation (FMD) and hyperemia flow at rest, during reactive hyperemia were assessed in brachial artery by high resolution,two dimensional ultrasonography. Results Brachial artery FMD of hypertensive patients was significantly lower than that of controls (9.8%±6.7% vs 14.7%±6.8%,p<0.01). Hyperemia flow of hypertensive patients significantly decreased compared with that of controls (529±114 mL/min vs 642±160 mL/min,p<0.01). FMD was negatively related to systolic blood pressure and diastolic blood pressure,respectively (r=-0.473,p<0.01 and r=-0.308,p<0.05). Hyperemia flow was negatively related to systolic blood pressure besides diastolic blood pressure. Conclusions Impaired endothelial function exists in patients with early hypertension without evidence of overt atherosclerosis.