AIM: To study the effects of gypenosides (Gyp) on lymphocyte transformation and DNA polymerase II activity. METHODS: Lymphocyte transformation response was induced by concanavalin A and lipopolysaccharides respectively. The activity of DNA polymerase II and DNA synthesis were assayed with TTP and [3H]TdR incorporation respectively in mixed lymphocyte culture test. RESULTS: Gyp 2.5-20 mg L-1 enhanced splenic T- and B- cell transformation, increased the DNA synthesis and potentiated the activity of DNA polymerase II. However, Gyp > 40 mg L-1 showed contrary effects. CONCLUSION: Gyp regulated lymphocyte transformation and DNA synthesis by regulating DNA polymerase II activity.