Components of the renin angiotensin system have been demonstrated in mouse and rat brains. However, local synthesis of renin has not been documented. In this study, we employed mouse submandibular gland renin complementary DNA (pDD-1D2) and rat liver angiotensinogen complementary DNA (pRang3) to examine whether renin and angiotensinogen RNA sequences exist in mouse and rat brains. Angiotensinogen messenger RNA sequences were readily demonstrable in whole rat and mouse brain using Northern blot hybridization analysis. Using large quantities (> 100 μg) of brain total RNA and the sensitive complementary RNA probe, we were able to detect low levels of renin RNA sequences in the brains of both species. The relatively low concentration of brain renin messenger RNA and high concentration of angiotensinogen messenger RNA raises several interesting questions about the distribution of these two proteins and their relative contribution to the activity of the brain renin-angiotensin system. In summary, our data demonstrate the expression of both renin and angiotensinogen genes in mouse and rat brains and provide definitive evidence for an independent endogenous brain renin angiotensin system.