We studied waking, ventilatory, and reflex tracheal smooth muscle (TSM) responses to tracheobronchial irritation or lung inflation in three sleeping dogs. The dogs breathed through a cuffed endotracheal tube, and airflow was measured with a pneumotachograph. TSM tone was monitored directly by measuring pressure in the water-filled cuff of the endotracheal tube. Mild degrees of tracheobronchia irritation, produced by squirting 0.1--1.0 ml of water into the lower trachea, or by having the dogs inhale one breath of acetic acid vapor (concentration 17 ppm), generally caused arousal from slow-wave sleep (SWS), but not from rapid-eye-movement (REM) sleep. During wakefulness the irritant stimuli caused coughing and TSM constriction; during SWS or REM sleep, these responses occurred only if the stimulus first produced arousal. In contrast, stimulation of pulmonary stretch receptors by lung inflation did not cause arousal, but readily produced apnea and TSM relaxation during SWS. The results indicate that cough and airway smooth muscle constriction in response to bronchopulmonary irritant stimuli do not occur in the absence of arousal, and that arousal responses to such stimuli are depressed in REM sleep.