It is well recognized that those cells, requiring protein synthesis as growing immature cells or the secretory gland cells, contain a large amount of RNA in their cytoplasm, thus ribonucleic acid in the cytoplasm plays a very important role in the protein synthesis. Altho ugh cerebral ganglion cells contain a fairly large amount of RNA in their cytoplasm, the cell growth, cell division and protein secretion are not usually observed in these particular cells. High level of RNA of the cerebral ganglion cells may have an intimate relation with the highly differentiated cell function of the cerebral ganglion. For the purpose to elucidate the high level of RNA in the cerebral ganglion cells and its function, the author injected ribonuclease into the brain and liquor of guinea pigs to decompose RNA in the brain tissue. The behaviors of the animal under these conditions were observed, and also histological examinations were performed with each animal. As the result the following points were clarified. 1) when over 1 mg of RNase was injected into the brain, it caused lytic change of RNA in the cerebral ganglion cells and functional disturbances such as immobility, but the animal still retained the orientation ability. 2) It was confirmed that neither reduction nor disappearance of RNA in the cerebral ganglion cells could be the real cause of the experimental guinea pigs. These results suggest that this method would serve adequately for the analysis of the role of RNA in the brain cells.