Allopurinol has been shown to have a protective effect on ischaemic tissue by the indirect prevention of excessive purine loss. This property was tested in the gerbil model of acute stroke. A total of 69 animals were pretreated with an intraperitoneal injection of either allopurinol (50 mg/kg) or sterile water and then subjected to unilateral ligation of the left common carotid artery under general anaesthesia. The clinical effect of the ligation was grouped into three categories of normal, mild to moderate defect (splayed leg, turning behaviour) and severe defect (death, nonresponsiveness and seizures). More normal animals and fewer severely affected animals were present in the allopurinol treated group compared to controls, but only at 2 to 4 hours after carotid ligation (p less than 0.05). Histological examination of brain tissue from the normal category failed to reveal any difference in subclinical ischaemic damage between the two groups. It was concluded that allopurinol may have a protective effect in acute stroke and that this property warrants further elucidation.