1. Localization of renin in rat and mouse brain was determined by immunohistochemical methods with specific anti-renin antibodies. 2. Renin-containing neuronal cells were found in the medulla oblongata, cerebellar nuclei and hypothalamus. Purkinje cells contained renin. 3. Glia-like cells contained renin. Some of them are closely associated with vascular walls and these vascular walls were renin positive. 4. The pineal gland, adenohypophysis and choroid plexus contained renin. 5. The extensive distribution of renin suggests functions other than those which have been associated with the hypothalamus.