Introduction: Endothelial dysfunction is essential in the pathogenesis of arterial hypertension (AH). The beneficial role of allopurinol (ALLO) on endothelial dysfunction is known, but the effect on functional vascular remodeling in relation to the severity of AH is not well studied. The purpose of the study was to evaluate the effect of ALLO on endothelial vasodilation function in patients (pts) with essential AH treated conventionally. Methods: In 103 pts with essential AH (grade II – 28%, grade III – 66%), mean age 62 ± 14 years; men 52%, treated according to ESH/ESC 2013 Guidelines, serum uric acid (SUA) and target organ damage (cardiac, renal, peripheral arterial and cerebral) were determined. 57 patients were randomized to receive ALLO 300 mg/ day (group ALLO +), regardless of the SUA level. In all patients (group ALLO + /group ALLO-) endothelial function was evaluated by flow-mediated vasodilation method (FMD) using two-dimensional vascular ultrasound of the brachial artery at inclusion, after one month and aft er three months. Data were statistically analyzed (Excel, Statistică). Results: Blood pressure (mm Hg) was 153 ± 27/91 ± 13 in ALLO+ vs 149 ± 23/88 ± 13 in ALLO-, p = 0.09, SUA (mg/dl) was 5.4 ± 1.7 in ALLO+ vs 5.2 ± 1.7 in ALLO-, p = 0.6, correlated to the number of risk factors – r = 0.34 p = 0.0004, to HeartScore – r = 0.32, p = 0.001, target organ damage – r = 0.35, p = 0.0003, left ventricular mass – r = 0.32, p = 0.0022, and FMD – r = -0.61, p = 0.044. Aft er 1 month SUA (mg/dl) was 3.3 ± 1.4 in ALLO+, p < 0.00001 vs 5.2 ± 1.7 in ALLO-, p = 0.94. In pts with moderate risk AH, FMD variation after 3 months was 1.29 ± 0.5 in ALLO+ vs 0.09 ± 0.42 in ALLO-, p = 0.00006, in pts with high risk AH aft er 3 months 1.49 ± 0.68 in ALLO+ vs -0.014 ± 1.06 in ALLO-, p = 0.0003, in pts with very high risk AH aft er 1 month 0.56 ± 0.28 in ALLO+ vs -0.009 ± 0.36 in ALLO-, p = 0.00002, after 3 months 2.41 ± 0.64 in ALLO+ vs 0.06 ± 0.49 in ALLO-, p < 0.00001. Conclusions: Data suggest that SUA correlates to (1) endothelial dysfunction, (2) the cardiovascular risk and (3) the target organ damage in patients with AH, and (4) allopurinol improves endothelial dysfunction as assessed by FMD regardless of the severity of AH. Acknowledgement: This paper is supported by the Sectorial Operational Programme Human Resources Development (SOP HRD) 2007 – 2013, financed from the European Social Fund and by the Romanian Government under the contract number POSDRU/107/1.5/S/82839.