Microinjection of serotonin directly into the nucleus tractus solitarius produced a dose dependent increase in arterial blood pressure of anesthetized rats. The serotonin antagonists BOL and metergoline significantly attenuated the serotonin pressor effect and the serotonin uptake inhibitor fluoxetine significantly enhanced the magnitude of the pressor response. Electrical stimulation of the dorsal raphe nucleus or microinjections of serotonin into the preoptic regions of the hypothalamus produced a transient rise in arterial blood pressure of both spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) controls. These effects can be attenuated by metergoline. These results demonstrate that serotonin can influence blood pressure at a number of brain sites known to modulate blood pressure in subjects with normal or elevated blood pressure.