More than 400 patients who had undergone a cerebrovascular attack or a transitory ischemic attack had bilateral measurements of regional C.B.F. by the 133 Xe inhalation technique and a gamma-camera. Inhalation of the air-Xe mixture in the closed spirometric circuit takes 1.5 mn at a concentration of 1 to 2 mCi/1. A very high resolution collimator allows a maximal counting rate of 300 000 i.p.m per hemisphere. At the opening of the circuit, the cerebral curves are analysed by the initial slope index (ISI) method, that index being obtained by deconvolution of the first 2.5 minutes of wash out. With this method, normal values are: 44,5 +/- 5ml/mn/100g. After calculation of hemispheric and regional ISI, we evaluate a regional partition coefficient (for total hemisphére) between tissue and blood with this formula: Formula: [See Text], being the activities counted at time t respectively in the area and on the hemisphere. Koh and Kor referring to ISI in total hemisphere (H) and area (r) C (a): arterial concentration A regional blood flow is obtained by Fr = 100 lambda rKor in a maximum of 16 different areas (with lambda n = 1ml/g) With our data processing system we get a functional image of r CBF which visualizes values of the (lambda r. Kor). In order to avoid statistical problems due to separate calculations of lambda r and Kor in very small areas we use a very simple kind of a functional image: subtraction of regional cerebral activity between time 0.5 and 1.5 mn and at 1.5 and 2.5 mn of wash out. We show that this image is correct display of regional inequalities of lambda rKor. In 48 cases of complete stroke comparison of the ISI index Kor and the ISI index Kor and the lambda r Kor referring to the area of maximal ischemia appearing on the functional image showed perfect correlation between the lambda rKor and the functional image; and only in 80% cases with the unique value of Kor. Those discrepancies between Kor and lambda rKor are related to necrosis and late revascularisation in cerebro vascular attacks.