Lipid peroxidation is a free radical process which is implicated in the formation of atherosclerosis. Vitamins C and E are important natural antioxidants which inhibit lipid peroxidation and a high intake of these vitamins, particularly vitamin E, is related to a reduced incidence of ischaemic heart disease. Hypertension is an independent risk factor for atherosclerosis and its relationship to antioxidant status is undetermined. In this study, we investigated free radical activity by measuring plasma malondialdehyde (MDA) using high-performance liquid chromatography (HPLC), vitamin C status measured as plasma ascorbic acid and vitamin E status measured as plasma lipid standardized alpha-tocopherol and erythrocyte alpha-tocopherol. We compared 28 patients with essential hypertension to 31 healthy subjects. Results showed that in comparison with the healthy subjects, the hypertensive patients had significantly higher plasma MDA levels (0.95 +/- 0.28 vs 0.69 +/- 0.21 mumol/l, mean +/- SD, p < 0.001) and significantly lower levels of plasma ascorbic acid (34.83 +/- 12.88 vs 51.76 +/- 13.34 mumol/L, p < 0.01). In addition, erythrocyte alpha-tocopherol concentration, which may reflect vitamin E protection in cell membranes, was significantly lower in hypertensive patients when compared with the normotensive controls (3.87 +/- 0.53 vs 4.82 +/- 1.01 mumol/l, p < 0.001), although plasma alpha-tocopherol levels were similar in the two groups (25.07 +/- 10.45 vs 23.96 +/- 6.07 mumol/l). Our results suggest that hypertensive patients may have increased lipid peroxidation and reduced protection from vitamins C and E. This may contribute to the propensity in such patients to develop atherosclerosis.