A major portion of renin-like activity in extracts of brain tissues is due to nonspecific action of proteases. True renin has been separated from the proteases by various affinity chromatographic methods and true renin was identified by its inhibition by specific antirenin antibodies. Brain renin has been purified to varying extents. Renin in bovine pituitary was completely purified. Certain properties of brain renin are different from renal renin. The presence of inactive prorenin was also found in many regions. Immunohistochemical studies with renin antibodies showed intracellular localization of renin in many regions of the brain. Renin was also localized in LH gonadotrophs in the adenohypophysis. Many cloned neuroblastoma cell lines contain not only renin but also all other components of the renin-angiotensin system, indicating the existence of an intracellular mechanism of angiotensin formation within neurons.