Apelin, an endogenous peptide exerts its actions through binding to its receptors (APJ receptors) and has been demonstrated in both animal and human studies to have inotropic, diuretic (nitric oxide-dependent), and vasodilator effects, in addition to antagonistic effects on angiotensin II. In this investigation, serum apelin, nitric oxide (NOx), sodium (Na) and potassium (K) were evaluated in patients with essential hypertension and compared to their levels in healthy subjects. Our results revealed a significant decrease in serum apelin in essential hypertensive patients compared to the controls (P < 0.0001). NO, Na and K increased in the patients compared to controls (P < 0.05). A weak positive correlation between serum apelinand NO (r = 0.185) and a significant negative correlation between both of Na and K and serum apelin (r = -0.526 & 0.269, respectively) was found in essential hypertensive patients.The study suggested that apelin may play a role in the pathogenesis of essential hypertension, possibly through affecting blood hemostasis.