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The Brachet-Pappenheim cytochemical RNA-detection method was used to reveal the localization of RNA in nuclear and cytoplasmic structures of secretory cells of the anterior pituitary in various functional states. The methyl green-pyronin staining standard procedure was slightly modified by changing the acidity of the stain mixture, prolonging the staining and differentiation time, and introducing iso-propyl alcohol in the differentiation. The main part of the RNA detected by means of pyronin was found to be distributed upon the predominantly acidophilic area. The pictures of RNA-localization, obtained in early, more advanced and final stages of the secretory act, were closely similar to those discovered in secretory cells of other glands, and in nerve cells, by ultraviolet absorption analysis. It is the first time properly with regard to the pituitary, that a similar, cytoplasmic protein synthesis indicating RNA-system, as a whole, could be revealed by means of Brachet-Pappenheim's cytochemical method. Relation of the RNA as to the various cell types in the pituitary, and to the appearance of phosphomonoesterases is discussed.