The correlation between the local cerebral blood flow (lCBF) and the specific gravity (SG) of the topographically corresponding cortical area was examined using a model of regional cerebral ischemia by means of transorbital occlusion of the middle cerebral artery (MCA) in cats. Cats were divided into the following experimental groups. Group A: two hours MCA occlusion followed by two hours recirculation; Group B: two hours MCA occlusion; Group C: four hours MCA occlusion. The lCBF and the SG were measured by the use of hydrogen clearance method and gradient column, respectively. Two hours MCA occlusion resulted in a moderate drop in SG in the cortical areas where the lCBF decreased below 20 ml/100g/min during ischemia (Group B). Four hours MCA occlusion in Group C resulted in a similar drop in SG. Two hours recirculation following two hours MCA occlusion in Group A, however, caused a remarkable drop in SG which was significantly greater than those in Group B and C. There was no correlation between the drop in SG and the level of post-ischemia lCBF (reactive hyperemia) in Group A. Thus, the present study revealed i) that the development of cerebral edema as evidenced by the drop in cortical SG was associated with an extreme reduction in lCBF, ii) that recirculation exerted a detrimental influence on the post-ischemic brain injury and iii) that the edema aggravation during recirculation was not necessarily dependent on the magnitude of reactive hyperemia. Based on the above results, it was suggested that the cause of edema aggravation following recirculation, namely the development of vasogenic edema, might reside in some chemical mechanism such as lipid peroxidation.