Protein B23/nucleophosmin is a polyfunctional protein existing in cells in numerous structural forms. In this work, for the immunochemical analysis of nucleophosmin we used the antibodies specific to different forms of nucleophosmin, namely, antibodies selectively revealing monomers of all the known forms of this protein and antibodies specific only to isoform B23.1. Homogenates of different rat tissues such as the brain, liver, kidney, lung and heart were used, as well as nuclei from liver and brain cells. For the first time, we show that the structural state of nucleophosmin in brain differs from its state in other tissues, including the liver that is enriched with nucleophosmin. It was revealed that on immunoblots of brain homogenates not only monomeric form of nucleophosmin but also unique SDS-resistant oligomeric forms were detected in the SDS-PAGE. Analysis of nucleophosmin in the cerebellum, cortex, amygdala, brainstem, and hippocampus showed that most enriched with nucleophosmin were hippocampus and cerebellum; on their immunoblots SDS-resistant oligomeric forms of nucleophosmin dominated. Using immunochemical analysis of the protein in primary cultures of cerebellum glial cells and neurons, significant structural differences of nucleophosmin in proliferating glial cells and non-proliferating neurons were revealed for the first time. It was found also that the nucleophosmin content in glial cells is much higher than in neurons and that the main forms of protein B23 in glial cells on immunoblots are the SDS-resistant oligomers, while a monomeric form was present in much smaller quantities. In contrast to glial cells, neurons did not contain such oligomers. In neurons, only trace amounts of a monomeric form of nucleophosmin were found, which were undetectable by the antibodies specific to isoform B23.1. © 2014 Pleiades Publishing, Ltd.