The studies described here have utilized electrical stimulation techniques to examine the effects of activation of neural elements within the area postrema (AP) on cardiovascular control mechanisms. A total of 45 urethananesthetized male Sprague-Dawley rats were used in these experiments. Low-frequency electrical stimulation (10 Hz, 200 microA) in the AP resulted in rapid onset (less than 2 s), short-lasting (less than 5 s after end of stimulation) decreases in mean arterial blood pressure (-34.8 +/- 2.7 mmHg, n = 17 rats). In contrast, similar stimulation in the adjacent nucleus tractus solitarius (NTS) caused similarly timed increases in blood pressure (+43.1 +/- 6.7 mmHg, n = 5 rats). Activation of neural elements within the AP was found to significantly (Student's t test, P less than 0.01) reduce heart rate, an effect that was also specific to the AP site as similar stimulation in the NTS was without effect. These data support an important role for AP in cardiovascular control mechanisms. They demonstrate that stimulation in AP results in rapid reversible decreases in mean arterial blood pressure and heart rate. Such findings further emphasise the potential roles of this circumventricular structure in autonomic control mechanisms.