The reactive microglias induced by 25 mu mol of beta -amyloid peptides (A beta 25-35) and/or IFN-gamma can initiate the microglial respiratory burst and release NO, respectively. Oxidative stress and inflammatory function have been implicated in Alzheimer's disease (AD). We showed that 10 mu mol 17-beta -estradiol (E-2) and 1-10 mu mol ginsenoside Rg(1) (Rg(1)) could prevent the toxicity of A beta 25-35 and/or IFN-gamma to microglias, inhibit the microglial respiratory burst activity and decrease the accumulation of NO. These results demonstrated the protectional effect of E-2 or Rg(1) on neuron from damaging by reactive microglias in AD.