The papers about cerebral blood flow (CBF) in patients with cerebrovascular diseases have been already reported by positron emission computerized tomography (PET), single photon emission computerized tomography (SPECT), Xray CT (CT) using cold Xe, and so on. However the literature about the CBF changes in acute stage is few. We studied CBF in 68 patients with ischemic cerebrovascular disease within 48 hours after the onsets from February 1984 through February 1985. CBF was measured by a rapidly rotating single photon emission computerized tomography (SPECT) using non-invasive Xenon-133 inhalation method. Our subjects included 51 cases with cerebral infarction (male 37, female 14, average 62.9 years) and 17 cases with TIA (male 13, female 4, average 60.5 years), the patients who had a past history of stroke were excluded from the subjects. The SPECT was performed with use of Tomomatic 64 developed by Dr. Lassen, et al, SPECT and carotid arteriography were simultaneously performed within 48 hours in all cases. CT we used were GE CT 9800 scanner and Hitachi HF CT. The following results have been obtained: 1) SPECT clearly showed an ischemic focus correlated with clinical symptom after the attack rather than CT, the positive finding by SPECT was 92.2% and that by CT was 62.7% within 48 hours after the onset. 2) The remote effect phenomenon so-called crossed cerebellar diaschisis was demonstrated in 7 of 14 cases (50%) with cerebral infarction due to internal carotid artery occlusion and in 9 of 26 cases (34.6%) with that due to middle cerebral artery occlusion. 3) SPECT and CT were performed within 8 hours after the onset in 20 cases with cerebral infarction. SPECT showed decreased CBF in all cases whereas the positive finding by CT was 40.0%. The area of decreased CBF was always larger than the low density area that CT demonstrated. Mean CBF value of the cerebral hemisphere in the cases with ICA occlusion within 8 hours after the onsets was 31.0 (ml/100 g/min), and that of MCA occlusion was 36.0 (ml/100 g/min), and that of MCA occlusion was 36.0 (ml/100 g/min). 4) The positive finding by SPECT on TIA cases was 47% and that by CT was 41.1%, SPECT usually did not demonstrate a small ischemic focus especially at the deep region (ie, basal ganglia region). 5) SPECT using Xe-123 inhalation was useful and non-invasive method for the diagnosis in acute stage with ischemic cerebrovascular disease.(ABSTRACT TRUNCATED AT 400 WORDS)