The present study describes the regional distribution and cellular localization of angiotensinogen-mRNA in the rat brain as investigated by means of in situ hybridization also in combination with immunocytochemistry for glial fibrillary acidic protein. The angiotensinogen gene expression seemed to be restricted to astroglia and showed marked regional differences. In some areas angiotensinogen-mRNA was present in almost all astrocytes with a strong signal (e.g. hypoglossal nucleus), whereas in other areas the angiotensinogen gene was expressed only in a certain population of glial cells. Some areas like the lateral septum were devoid of any detectable angiotensinogen-mRNA. A semi-quantitative atlas of the regional distribution of brain angiotensinogen-mRNA was obtained by using computer-assisted microdensitometry and revealed considerable rostro-caudal fluctuations of the angiotensinogen-mRNA content of certain regions (e.g. the subfornical organ). Furthermore, a semi-quantitative analysis on the cellular level of angiotensinogen gene expression was performed showing a correlation of the angiotensinogen gene expression to the glia content of the regions examined. It was also demonstrated that the angiotensinogen gene expression had its highest levels in several distinct areas of the brain (e.g. the preoptic region and the hypothalamus), whereas other areas showed only low to moderate levels (e.g. the thalamus). The expression of the angiotensinogen gene in the rat brain was not only restricted to areas involved in cardiovascular and neuroendocrine control, but was also present in functionally different regions. Our data thus indicate that, based on the regional distribution of angiotensinogen-mRNA, angiotensin peptides may have other functions besides participation in cardiovascular and neuroendocrine control.