Using the method of immunocytochemical staining in the reaction of indirect fluorescence employing affinity purified antipeptide antibodies specific for monomeric forms of the protein B23 (AT 19-36) and antibodies against oligomeric forms (AT 283-294) that selectively detect the isoform B23.1 we conducted a comparative study of the lymphoid cells of the patients with various lymphoproliferative diseases and patients with diseases of nononcological nature in comparison with intact lymphocytes of the healthy people. It was established that in lymphoproliferative diseases with a low degree of proliferative activity of the cells that is assessed by the levels of Ki-67 positive cells and in the diseases of the blood of nononcological nature localization of monomeric and oligomeric forms of the protein B23 revealed with both antipeptide antibodies in lymphoid cells was similar to their localization in the lymphocytes from the healthy people. In malignant lymphoproliferative diseases that are characterized by a sharp increase in the proliferative activity of the cells it was revealed for the first time using immunocytochemical study of lymphoid cells with AT 283-294 (that specifically stains SDS resistant oligomers on western blots) that the intensity of the staining increases and on top of that the number of stained nucleoli increases as well (from 1 to 3 and more) and their size and shape change in contrast to the nucleoli stained with monomers revealed with AT- 19-36 that are localized in the cytoplasm and nucleoplasm and that don't undergo considerable changes during the progression of lymphoproliferative diseases. The obtained results point to the high value of the immunocytochemical study of oligomers that contain the isoform of the protein B23.1 that specifically stains AT 283-294 that localizes in the nucleoli of cells and changes in the process of proliferation that reflects the degree of proliferative activity of cells.