Background Oxidant stress is implicated in the pathogenesis of atherosclerosis in cardiovascular diseases. Our aim was to test oxidative stress, as 8-iso-prostaglandin F2 alpha (8-iso-PGF2 alpha), and its relationship with inflammation markers C-reactive protein (CRP) and tumour necrosis factor-alpha (TNF alpha), and endothelial activation assayed as soluble intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 in essential hypertension. Methods In 216 essential hypertensive patients and 55 healthy control individuals, plasma levels of high-sensitivity CRP and TNF alpha, 8-iso-PGF2 alpha, ICAM-1 and VCAM-1 were measured in basal conditions. Moreover, basal and 24-h ambulatory blood pressure monitoring measurements were obtained. Results Essential hypertensive patients showed higher levels of 8-iso-PGF2 alpha (P < 0.0001), high-sensitivity CRP, TNF alpha, ICAM-1 and VCAM-1 (P < 0.001, respectively) than control individuals. In control individuals, 8-iso-PGF2 alpha correlated only with high-sensitivity CRP (P < 0.001). In essential hypertensive patients, 8-iso-PGF2 alpha correlated with high-sensitivity CRP (P < 0.000001), TNF alpha (P < 0.0001), ICAM-1 (P < 0.000001), VCAM-1 (P < 0.0001) and blood pressure. The multiple regression analysis considering 8-iso-PGF2 alpha as the dependent variable showed that in essential hypertensive patients the independent predictors of 8-iso-PGF2 alpha were ICAM-1, high-sensitivity CRP (P < 0.00001, respectively), and TNF alpha (P=0.028). Conclusion Our findings demonstrate that oxidant stress is increased in essential hypertension, and relates to inflammation and endothelial activation. Factors other than blood pressure are stronger predictors of oxidant stress. J Hypertens 25:423-428 (c) 2007 Lippincott Williams & Wilkins.