Stereotaxic thalamic lesions by electrocoagulation have been produced on sixty four cases of extrapyramidal disorders by means of newly deviced simple electrocoagulation probe, which is made of 300mm of straight steel wire with one millimeter in diameter covered loosely by 293mm of hard teflon pipe as insulation to electricity and the local heat. The probe, therefore, has retractable 7mm bare tip, so it can be safely withdrawn without any, danger from hemorrhage of destructed tissue after coagulation. As a preliminary experiment, stereotaxic thalamic lesions by the probe have been produced in the dog brain as well as the formalin suspended human brains under observation with ultrasonic A-scope apparatus by reflection method. The transducer provided with barium titanate (2.25 Mc, 10mm diameter) was used. It was clearly identified that the echoes were corresponded to size and location of the lesions in the dog brain as well as human brain specimen. During the surgery, echo was noted from the tip of probe which was in the target area of the thalamus of the patients. In every case, the lesion echoes showed high fluctuating amplitude and width during coagulation procedure. Lesion echoes were observed up to 45 days after the surgery. They maintained stable duplicate echoes during the period. It is our suggestion that the ultrasonic examination of the stereotaxic lesion is useful to note accidental hemorrhage in the lesion of a reconvalescent patient. It is also a great aid for this purpose to check the midline echo at the same time. Recently further investigations with ultrasonic compound sector scope, Aloka SSD-10, were done. The ultrasonic scanning was performed on the operative side vertically. During and after the coagulation of the target, twenty three cases were examined with compound sector scope. The reflextion from the lesion with compound scope was noted in 91.3% of the cases while 82.9% with A-scope. The lesionecho was obtained about 1.4cm lateral from the midline echo in case of destruction of V.L. nucleous of the thalamus. In case of the centre median the lesionecho was located adjacent to the midline echo. These lesionechoes were located correctly in their anatomical coordinates of the targets. But the size and shape of the lesionechoes were identified rather larger than the destructed lesions. This deflexion would be due to the width of the ultrasonic reflected wave. As confirmative experiments, stereotaxic thalamic destructive lesions have been produced in the specimen of the formalin suspended human brains under observation with ultrasonic compound sector scope. It is our impression that echo-encephalgraphy with the ultrasonic compound scope has a potential usefulness to observe location, shape and size of the lesion as well as to detect the accidental hemorrhage of a reconvalescent patient.