Changes in endotracheal tube cuff pressures produced by bucking and laryngospasm caused by endotracheal aspiration and movement of the tube in the trachea have been investigated in 100 cases. Cuff pressures were increased significantly by 12.3+ 1.3 and 14.7 + 1.4 mmHg respectively with bucking and endotracheal aspiration. There was no changes in cuff pressures with the mode of respiration and muscle relaxant used. Endotracheal aspiration or changing the position of the tube in trachea that may cause bucking and laryngospasm should be carried out while the patient is still under the effect muscle relaxant or after celeaning the mouth and pharynx and deflating the cuff.