Continuing their study of 1993 on polyploidy in human cardiac muscle and on related phenomena in some other living organisms, the authors decided to investigate the phenomenon of polyploidy in cells of the CNS. Research findings reported by many authors, especially by Sandritter et al., tetraploidy (4c) is present in the Purkinje cells (in the cerebellum) and in pyramidal cells of the hippocampal gyrus, from the early stages of the ontogenic development until the end of life. According to the authors, this particular feature of the Purkinje cells (4c) may be related to their intense function. The cells are characterized by a lack of lipofucsine, and in pathological conditions no fat substances are deposited there. Moreover, the cells in question are highly sensitive to various noxious factors, such as hypoxia, alcohol or arsenic. They are the first to be affected by such harmful influences.