Nitroglycerin is a vasodilator which induces vascular relaxation by releasing nitric oxide in the wall of blood vessels. It has been suggested that the cardiovascular inhibitory responses which are induced by this drug are mediated by central structures. In this study, we evaluated the distribution and intensity of Fos immunoreactivity in rat brain nuclei following the systemic administration of nitroglycerin. In the medulla, a significant number of Fos-immunoreactive neurons were observed in the nucleus tractus solitarius, ventrolateral medulla, area postrema and spinal trigeminal nucleus caudalis. A robust staining was seen in the parabrachial nucleus, locus coeruleus and ventrolateral periaqueductal grey. In the hypothalamus, Fos-positive cells were densely packed in the paraventricular and supraoptic nuclei. Other areas where significant staining was observed include the central nucleus of the amygdala and the subfornical organ. These findings demonstrate that the systemic administration of nitroglycerin is capable of activating a spectrum of functionally diverse brain regions. This spectrum includes areas involved in reflex adjustments to nitroglycerin-induced hypotension, areas involved in sensory nociceptive perception and areas associated with integrative regulation of autonomic, behavioral and neuroendocrine functions.