When staining the neurosecretory cells with N,N′-diethylpseudoisocyanine chloride according to Sterba fluorescence of nucleolus and structures in the peripheral zone of the cytoplasm was observed simultaneously with the fluorescence of the neurosecretory granules. Preliminary treatment of sections with ribonuclease made it possible to obtain preparations in which only neurosecretory granules fluoresce in the neurosecretory cells. It proves that the secondary fluorescence of the peripheral structures is due to the ribonucleic acid they contain, and the structures themselves are Nissl's substance. The intensity of the secondary fluorescence of the neurosecretory substance and the Nissl's substance changes when embedding sections stained with N,N′-diethylpseudoisocyanine chloride in media with different pH values (from 2.6–8.9), these changes being different for each of these components. The most striking contrast between the fluorescence of the neurosecretory substance and the rest of the structures of the cell was observed in the pH 4.0–4.9 region. Especially stable preparations can be obtained by using a stain diluted with a buffer with pH about 4.5. The proposed modification of the method makes it possible to obtain preparations with more striking electivity of the secondary fluorescence of the neurosecretory substance than when using original method of Sterba.