Plasma levels of thiobarbituric acid reactive substances (TBARS) were measured as an indicator of lipid peroxidation, in 14 patients suffering from tardive dyskinesia (TD). There was a highly significant positive correlation between plasma TBARS (both basal and iron stimulated) and severity of TD. Patients were then treated for 1 month with the free radical scavenger vitamin E (1200 i.u. daily). Following vitamin E treatment, there was a clinically and statistically significant amelioration of TD, and this improvement was maintained at follow-up 7-13 months later. There was no consistent or significant change in plasma TBARS levels related to treatment with vitamin E.