The purpose of this study was to examine the effect of extracorporal collateral circulation (ECCC) between the femoral and the external artery (ECA) on the cerebral circulation, in experimentally induced ischaemia, in rabbits. The animals were divided in four groups. Seven animals (Group A) were used to determine the injection pressure (150-160 mmHg) at the ECA, necessary to achieve collateral circulation between ECA and internal carotid artery (ICA), after occlusion of ICA. Group B (8 rabbits) was the control group for establishing cerebral ischaemia (CI) by a) ligating the common carotid artery bilaterally, b) coagulating the right vertebral artery and c) exsanguinating the animal (removing 28-30 ml of blood). The induced ischaemia was studied by BP and PCO2 monitoring, CBF measurement, videomicroscopy of surface cerebral vessels, and finally macroscopic and microscopic examination of brain sections. In group C (8 animals)-moderate degree of CI-brain circulation improved in all animals after the application of the ECCC, installed at 135 min after the onset of CI. In 10 animals (group D) with severe and prolonged (225 min) CI, ECCC enhanced the brain circulation in eight animals to a variable degree.