Report on 71 successful intraoperative sonographies. The advantages of the technique were particularly evident when searching for tumours which were not visible from the brain surface. In these conditions intraoperative sonography greatly facilitates the planning of the operative approach. The ultrasound examination allows to distinguish tumour from peritumoral edema and healthy tissues. In one case it proved superior to nuclear magnetic and computer tomography in determining extent and infiltration. The technique proved nearly indispensable for intraoperative puncture.