The activation of a DNA polymerase delta (pol delta) purified from bovine placenta by ginsenosides from Panax Ginseng C. A. Meyer has been studied. Preincubation of the enzyme with ginsenosides increased the polymerase activity 2.2-fold in a dose-dependent manner. There was a reproducible decrease in Km, in addition to a substantial increase in Vmax, in response to increasing concentrations of ginsenosides. Ginsenosides also activated the proofreading ability of 3'- to 5'-exonuclease activity associated with DNA pol delta. The coordinated activation of both polymerase and exonuclease activities of DNA pol delta by ginsenosides is consistent with the view that its polymerase and its exonuclease activities residue on the same protein molecule. UV/Vis difference spectroscopic studies suggested that the activation of DNA pol delta by ginsenosides might be due to the conformational change induced by ginsenosides binding.