The IgE content in both cytoplasm and culture medium of U 266 myeloma cells, was studied by the enzyme-linked immunoassay in correlation with Ag-staining of NORs of chromosomes in their nuclei throughout 9 days after cell seeding. Proliferative activity of the cells was evaluated with ³H-thymidine labeling. The average values of both the cytoplasmic IgE content and its secretion level in U 266 cell population, being in logarithmic growth phase, were higher in S-phase cells as compared with G₁-cells. On comparison of results of the present and previous (Turilova et al., 1998) studies it was revealed that U 266 myeloma cell line had a high stability of cell proliferation kinetics and IgE secretion and the dynamics of Ag-NORs-staining, while the number of argentophilic grains in the cell nuclei in the present experiment was higher to correlate with an enhanced IgE production. It is suggested that Ag-NORs-staining reflects the level of specific functional activity of cells in the U 266 line.