OBJECTIVE Several studies have shown that angiotensin II receptor blockers (ARBs) improve endothelial function and arterial stiffness. Telmisartan is a highly selective ARB that activates peroxisome proliferator-activated receptor gamma (PPARgamma). The purpose of this study was to evaluate the effects of telmisartan, such as endothelial function, arterial stiffness, and insulin sensitivity, in patients with essential hypertension. METHODS Thirty-nine patients with essential hypertension were administered telmisartan (80 mg once daily) using an open-labeled and prospective protocol. The patients were examined before and 8 weeks after treatment to assess changes in flow mediated-vasodilation (FMD), pulse wave velocity (PWV), quantitative insulin-sensitivity check index (QUICKI), homeostasis model assessment (HOMA), and adiponection. RESULTS The systolic and diastolic blood pressure (BP) decreased from 153+/-15 mmHg and 90+/-13 mmHg to 137+/-16 mmHg and 84+/-10 mmHg after telmisartan treatment, respectively (p<0.01). Telmisartan therapy increased the FMD from 7.6+/-3.5 to 9.0+/-2.8% (p<0.01). The following parameters of arterial stiffness were significantly improved after telmisartan therapy: brachial-ankle pulse wave velocity (baPWV), from 17.2+/-3.1 to 15.9+/-2.6 m/sec; heart-carotid PWV (hcPWV), from 9.7+/-1.8 to 9.0+/-1.9 m/sec; and heart-femoral PWV (hfPWV), from 11.3+/-1.9 to 10.7+/-1.9 m/sec (p<0.01). There were no changes in QUICKI, the HOMA level, and plasma adiponectin (p=NS). CONCLUSIONS These results suggest that telmisartan is effective in improving endothelial function and arterial stiffness in patients with essential hypertension.