Changes in the immunoglobulin synthesis in mouse hybridoma 1F7cell line following exposure to the anticancer drug adriamycin were studied. It was shown that adriamycin in concentrations up to 0.1μg/ml causes dose-dependent reversible enhancement of immunoglobulin heavy γ2bchain synthesis, and to a lesser extent, κ light chain synthesis. Enhancement of γ2bheavy chain synthesis accompanies an increase in Ig γ2bmRNA levels. Enhancement of DNA-binding activity of another B-cell specific protein, octamer transcription factor Oct-2 was also observed. Cell cycle analysis revealed accumulation of the ADR-treated cells in G2/M phase of cell cycle. These changes in hybridoma cells preceded the onset of internucleosomal DNA fragmentation and appearance of morphological characteristics of apoptosis. These findings suggest, that differentiation-related processes occur during the latent phase of apoptosis induced by adria-mycin in mouse hybridoma cells.