In order to know the possible involvement of the central angiotensin system in hypertension, angiotensinogen mRNA (AomRNA) levels of eight discrete brain areas were measured by Northern blot hybridization analysis in the spontaneously hypertensive rats (SHR), compared with those in age-matched normotensive Wistar-Kyoto rats (WKY). In 16-week-old SHR (hypertensive stage), AomRNA levels in the preoptic area (POA), but not in the ventromedial hypothalamus, lateral hypothalamus and mammillary body, among the hypothalamic nuclei, were higher (approximate 50%) than in WKY. There were no differences in other brain areas, such as the striatum, septum, amygdala and cerebellum between both the strains. The AomRNA levels in POA were already higher (38%) in 4-week-old SHR (prehypertensive stage) without significance, and the difference was augmented (82%) in 7-week-old SHR (evolving stage). These results suggest that the developmental changes of AomRNA levels at POA may be related in some aspect to hypertension process.