Plasma levels of the oxidants xanthine oxidase, nitric oxide and malondialdehyde and the antioxidants superoxide dismutase, glutathione peroxidase and glutathione reductase, together with total superoxide scavenger activity and non-enzymatic superoxide scavenger activity, were determined in 19 patients with acute ischaemic stroke and 20 controls. Compared with controls, superoxide dismutase, total superoxide scavenger activity, glutathione peroxidase and glutathione reductase activities were significantly lower, and nitric oxide and malondialdehyde levels significantly higher, in acute stroke patients. Xanthine oxidase showed a slight but non-significant increase in stroke patients compared with controls. There was no significant difference in non-enzymatic superoxide scavenger activity between the two groups. There was a positive correlation between glutathione reductase levels and Glasgow Coma Scale scores, and a negative correlation between malondialdehyde levels and non-enzymatic superoxide scavenger activity. These findings suggest that oxidative stress in patients with acute ischaemic stroke may be the result of an imbalance in oxidant/antioxidant homeostasis. Copyright © 2006 Cambridge Medical Publications.