Activity of bulbar respiratory neurons was recorded extracellularly in anesthetized cats in which sniffs were induced by mechanical stimulation of the nasopharyngeal mucosa during the expiratory pause. Sniffs were indicated by brief, rapid activation of the diaphragmatic EMG which was followed by a sharp rise of tracheal inspiratory airflow (aspiration reflex of Tomori). In large sniffs, inspiratory neurons were activated in highfrequency bursts which preceded diaphragmatic activation. Other neurons in the bulbar reticular formation did not exhibit these properties. Inspiratory neurons located ipsilateral to the stimulated nasopharynx in the region ventrolateral to fasciculus solitarius exhibited low-threshold bursting and the earliest activation. The same neurons responded weakly and late to stimulation of the contralateral nasopharynx. Inspiratory neurons located in the environs of nucleus ambiguus frequently failed to participate in weaker sniffs, but a few always participated. Most neurons in this region were activated at nearly equal times before the diaphragm whether ipsilateral or contralateral nasopharynx was stimulated. Expiratory neurons located bilaterally near nucleus ambiguus were inhibited in numbers and in degree which matched the magnitude of the sniff. Weaker sniffs were accompanied by inhibition of late expiratory units alone, while stronger sniffs involved all expiratory neurons. Repeated stimulations could silence the expiratory units for long periods.