Protein B23/nucleophosmin is a multifunctional protein existing in cells in numerous structural forms. In this work for immunochemical analysis of nucleophosmin we used the antibodies specific to different forms of nucleophosmin: antibodies selectively revealing monomers of all the known forms of protein B23 and antibodies specific only to isoform B23.1. Homogenates from different rat tissues such as brain, liver, kidney, lung and the heart were used, as well as nuclei from liver and brain cells. It was shown for the first time that the structural state of nucleophosmin in the brain cells differs from its state in other tissues including liver enriched with nucleophosmin. Immunochemical analysis showed that in contrast to other tissues, immunoblots of brain cells contained not only monomeric form of nucleophosmin but also unique oligomeric forms detected in the SDS-PAGE. Analysis of nucleophosmin in the cerebellum, cortex, amygdala, stem, and hippocampus revealed that most enriched with nucleophosmin are hippocampus and cerebellum. The SDS-resistant oligomeric form of nucleophosmin dominated in their immunoblots. Immunochemical analysis of the protein in primary cultures of cerebellum glial cells indicated that nucleophosmin exists in these cells in different states and revealed structural differences of nucleophosmin in proliferating glial cells and non-proliferating neurons. It was found nucleophosmin content in glial cells is much higher than in neurons. The main forms of the protein in glial cells on immunoblots were SDS-resistant oligomers, while a monomeric form was present in much smaller amounts. In contrast, neurons did not contain such oligomers. In neurons only a trace amount of a monomeric form of nucleophosmin was found, which was not detectable by the antibod ies against isoform B23.1.