To prevent the pseudomembranous laryngotracheitis cares should first be taken against infection complete sterilisation of the tube and choosing suitable size of the tube, administration of antibiotics before operation, avoiding the trauma of mucous membrane of the trachea by tube, keeping the cuff pressure necessarily minimum and choosing the kind of the lubricant may be necessary. Namely to choose the tube, the lateral view of X-ray is profitable and the cuff pressure about 30 mmHg may be suitable by low tension cuff. For the lubricant xylocainjerry is most useful and administration of antibiotics may be more effective. Using the above mentioned condition we performed experimentally 20 cases of endothracheal anesthesia and found no pseudomembranous laryngotracheitis at all. In preliminary experiment the pressure of the cuff upon the wall of the trachea and the relationship of the cuff pressure to the space between the tube and the trachea were studied.