Intra operative Doppler has been already used especially during cerebral vascular malformations surgery. The systematic practice of this method, in 15 cases, for the blood flow study of the sub millimetric cortical vessels is helpful, very simple, and harmless. The investigation has been achieved by the direct application of a sterilized 8 MHZ, 5 mm Doppler probe on a small cortical artery. As the diameter has been exactly measured (0,8 mm +/- 0,2 in 15 cases) it is easy to calculate the blood flow from the recorded curve diagrams. The normal cortical flow of the sub millimetric arteries is about 2,52 cm3/mn +/- 1,16 confirming the previous data obtained with other methods of approach. The study of contused brains, points out, the disastrous effect of edema on cerebral blood flow, which before a complete arrest, looses its continuous diastolic pattern. Deep seated angiomas can be accurately located together with the flow direction in their feeding vessels. This method is also of fair interest for extra intra-crânial anastomosis, the choice of the cortical artery for bypass and its functional appreciation.