Larynx resistance changes during the respiratory cycle at rest and after mechanical stimulation of the epithelium on different zones of the upper airways (extrathoracic trachea, glottis, nasopharynx) were studied in the dog by isolated glottis in situ technique. In reposed breathing, the increase in larynx resistance always started when inspiratory airflow reached its maximum value. Resistance remained high during expiration and had its lowest value when expiratory airflow decreased towards zero. The electromyogram reading for the abdominal muscle evinced low or no activity during the smaller larynx resistance period. The extrathoracic trachea mechanical stimulation with cough response was determined by a significant decrease of larynx resistance. There was also a significant increase in expiratory airflow and abdominal pressure. Inspiratory and expiratory total lung resistance values were both significantly increased with regard to reposed breathing. Mechanical larynx stimulation determined reflexive closing of the glottis, expiratory apnea, minimal abdominal pressure. No potentials were formed in the expiratory abdominal electromyogram. The response was similar to a spontaneous swallowing. Larynx resistance reached its minimal value before the expiratory airflow reached zero. Mechanical nasopharyngeal stimulation significantly increased larynx resistance.