Thirty cases of brain tumors, encephalomalacia and brain contusion were investigated by Aird's method. (1) The fact that the result of diagnosis localizing the lesion by this method was correct at 100% of all cases except the midline tumors such as hypophyseal tumors, was ascertained by operation. (2) After the operation, the cases, in which the-tumor was completely excised and clinical symptoms recovered, presented normal encephalogram. Therefore we have known, that it excellent value for judgement of the effect of therapy. (3) It is clarified experimentally, that the basic abnormat waves in brain tumors consist slow waves with 3-4-5 cycles, and the slow waves with 6-7 cycles are caused by brain swelling. (4) This method is extremely valuable for the diagnosis and the judgement of the effect of therapy of brain tumors, encephalomalacia and brain contusion etc.