Hypertension is associated with an increased risk of atherosclerosis. Free radical oxidative damage has been implicated in the atherogenic process. We measured levels of the antioxidants uric acid, thiols, vitamins C, A and E as well as the total antioxidant capacity in 21 normotensive controls, 22 patients whose hypertension was controlled on drugs and 30 patients with uncontrolled hypertension. Mean BPs in the groups were 125/76, 132/80 and 181/98 mmHg, respectively. When compared with controls, both hypertensive groups had significantly lower serum ascorbic acid (54 +/- 5 vs. 37 +/- 6 vs. 38 +/- 5 mumol/l, P < 0.05) and albumin-corrected thiol levels (9.91 +/- 0.18 vs. 8.69 +/- 0.20 vs. 8.92 +/- 0.19 mumol/g, P < 0.05). The levels of the other antioxidants did not differ significantly between the groups. Levels of von Willebrand factor, a marker of endothelial damage, were correlated with SBP but not with antioxidant status. We conclude that hypertensive subjects have lower levels of the antioxidants vitamin C and thiols and this may reflect greater oxidative consumption. The implications for atherogenesis and endothelial function and integrity in hypertension are discussed.