Mongolian Gerbils (Meriones Unguiculatus) are characterized by frequent anomalies of the circle of Willis. Their cerebral vessels lack arterial communication between the cerebral and vertebral system and they present an experimental model for cerebral ischemia. Among drugs which interfere with biogenic amine turn over, only 5HTP (75 mg/kg) decreased significantly the mean "stroke index". Vincamine (50 mg/kg) had the same effect.