To demonstrate the effect of diaschisis in acute unilateral cerebral infarction, the changes of regional cerebral and cerebellar blood flow(rCBF) following experimental occlusion of one middle cerebral artery(MCA) were studied in 15 mongrel cats, following occlusion of left MCA by coagulation using transorbital approach, rCBF's of both MCA trerritories and both cerebellum were measured simultaneously by the hydrogen clearance technique. Sham operation group consisted of 5 cats, in which transorbital exposure of left MCA was performed and the rCBF's were measured in the same manner as the experimental group without cauagulation of left MCA. After measurement of rCBF for 8 hours at fixed intervals, the animals were sacrificed and immediately thereafter 25 ml of 2% triphenyl tetrazolium chloride(TTC) solution was injected through each common carotid artery. The brain was removed and immersed in 10% buffered fomalin solution for two weeks, then the coronal plane through optic chiasm was examined for the cerebral infarction. As results, contralateral MCA territory and both cerebellum showed diaschisis after occlusion of left MCA, and contralteral cerebellar rCBF decreased more, showing characteristics of crossed cerebellar as well as interhemispheric diaschisis. Sham operation group showed no infarction, and in experimental group 40.2+/-1.3% of the coronal plane through the optic chiasm was infracted, showing high percentage of infarction with small standard deviation.