Local cerebral blood flow (1CBF) was measured autoradiographically 60 minutes after 15 minutes of forebrain ischaemia in rats treated with superoxide dismutase (SOD) before (50 mg.kg-1 body weight) or at the end of the ischaemia period (4 mg.kg-1 body weight). Incomplete forebrain ischaemia was produced by a combination of common carotid artery occlusion and bleeding to a mean arterial blood pressure of 50 mmHg. During ischaemia the 1CBF values in cortical areas were less than 3% of the preischaemic values and treatment with SOD prior to ischaemia did not influence 1CBF during ischaemia. Sixty minutes after termination of cerebral ischaemia the 1CBF values were decreased to between 40 and 60% of values found in control animals. Neither form of treatment improved the postischaemic cerebral blood flows. The results imply that postischaemic flow disturbances in the brain may not be due to extracellular superoxide production.