['Natural medicines derived from plants are drawing more and more interest in the prevention and treatment of diseases because of their unique characteristics, which include having fewer adverse effects and being more suitable for long-term use compared with synthesized chemicals. To explore the potentially health-promoting role of genistein, we used a rat model of rheumatoid arthritis (RA) induced by a subplantar injection of collagen.', 'In collagen-induced rheumatoid arthritis (CIA) rat model, their immunomodulatory activity on rat peripheral blood mononuclear cells (PBMC) was evaluated. Lymphocyte transformation was evaluated by MTT immunoassay, secretion of interferon-gamma (IFN-gamma) and interleukin 4 (IL-4) by enzyme-linked immunosorbent assay (ELISA), and expression of T-bet and GATA-3 by PCR.', 'The results showed that genistein modulated a Th1-predominant immune response because they significantly suppressed the secretion of IFN-gamma and augmented the IL-4 production, showed its immune modulation role of keeping the Th1/Th2 balance.'] Do genistein modulate immune responses in collagen-induced rheumatoid arthritis model?