It has been suggested that Tardive dyskinesia (TD) is associated with abnormal glucose metabolism. To investigate further the issue the effects of alloxan-induced hyperglycemia on the incidence and severity of haloperidol-induced perioral movements were studied in the rat. Hyperglycemic rats showed significantly higher incidence and severity of rating of abnormal perioral movements than did control rats. Severity ratings of perioral movements were significantly correlated with blood glucose levels in the hyperglycemic rats. These findings suggest that hyperglycemia may increase the severity of neuroleptic-induced perioral movements, and support the possibility that glucose intolerance may increase the risk of TD.