Electrical stimulation of the ventromedial region of the rostral fastigial nucleus (FN) in the cat produced marked quantifiable changes in respiration that were highly correlated with the concurrently elicited cardiovascular responses. The threshold- and stimulus-response curves were very similar for the two responses. Stimulation at relatively low frequencies produced increases in respiratory rate at all active sites. At approximately half the sites biphasic responses were observed with increases in stimulus frequency. These were characterized by a transient period of apnea beginning with onset of the stimulus, followed by an increased respiratory rate. At the remaining sites respiratory rate increased at all stimulation frequencies tested. Inspiratory duration decreased, and mean inspiratory flow increased. Tidal volume was not significantly altered. Similar changes were also observed when the pressor response was blocked by phenoxybenzamine. These observations, together with the frequent demonstration of expiratory-to-inspiratory and inspiratory-to-expiratory phase switching with short-burst stimulation, suggest that the FN can influence a respiratory central pattern generator. Based on these findings, a possible role for the FN in integrating cardiovascular and respiratory responses is suggested.