To determine whether the Hering-Breuer inflation reflex could be demonstrated in the presence and absence of behavioral influences on breathing, lung inflation was performed via the tracheal stoma in eleven laryngectomized subjects: seven seated at rest with their eyes closed and six recumbent during their deepest non-rapid eye movement sleep. Laryngectomized subjects were chosen for study since their permanent tracheal stoma and absence of a glottis abolished the sensation of inflation in the upper airways, avoided problems with glottic closure and allowed simple, airtight connection to respiratory apparatus. At rest awake, inflation volumes of 500-3050 ml caused no reproducible apnea. During EEG-documented sleep, the inflation reflex was tested on 75 occasions using inflation volumes of 540-2100 ml. On the 66 occasions not associated with subject arousal inflations exceeding approximately 1 L produced apnea terminated by inspiration; greater volumes gave longer apneas. At the end of the study the subjects were woken and retested; no reproducible apnea was found. We conclude that the Hering-Breuer inflation reflex can be demonstrated above the resting tidal volume range in adult man in the absence of the behavioral control of breathing.