Experiments using excised canine larynges and experimental air tract fluid were conducted to clarify the movement of air tract fluid in association with vocal fold vibration by means of X-ray stroboscope system. It was thought that the movement of air tract fluid in lubricating of the larynx during phonation was closely correlated to vocal fold vibration, especially the wave motion of the mucous membrane of the vocal folds and the movement of air tract fluid on the glottis might be one of parameters to evaluate the flexibility of the mucous membrane of the vocal folds.