Objectives:To investigate the occurrence of enhanced low-density lipoprotein (LDL) oxidation as an additional factor promoting atherosclerosis progression in hypertensive patients.Design:The oxidation of plasma LDL was investigated in a group of untreated patients with mild-to-moderate essential hypertension without clinically evident target organ damage and in a group of control subjects.Methods:LDL oxidation was evaluated as both the susceptibility to oxidationin vitroand the presence of plasma anti-oxidized LDL antibodies (as an index for oxidationin vivo).Results:LDL from hypertensive subjects exhibited enhanced susceptibility to oxidationin vitroas revealed by early and accelerated generation of conjugated dienes after exposure to CuSO4. Vitamin E concentration in LDL from hypertensive subjects was slightly but significantly decreased and its efficiency in protecting LDL from oxidation was impaired. Furthermore, a higher plasma anti-oxidized LDL titre was found in hypertensive patients. Subclass analysis revealed that the contemporary presence of hypercholesterolaemia did not significantly modify either the increased susceptibility of LDL to oxidation or the presence of plasma anti-oxidized LDL antibodies detected in hypertensive patients. Moreover, no correlation was found between LDL oxidation parameters and blood pressure values.Conclusions:LDL from hypertensive patients is more susceptible to oxidationin vitroand is more promptly oxidizedin vivo. These findings suggest a possible participation of LDL oxidation in promoting and accelerating the atherosclerosis that often develops in hypertensive patients.