beta-amyloid peptide (Abeta) consisting of 40 to 42 amino acid is the principle constituent of senile plaques in Alzheimer's disease. Although, the hypothesis that deposition of AP triggers a cascade of events leading to the pathology of Alzheimer's disease has been widely accepted, direct evidence for triggering accumulation of phosphorylated tau in paired helical filament is rare. In this study, we examined neurotoxicity induced by 3 kinds of beta-amyloid peptides 1 ~28, 25~,35 and 1~40 to elucidate the way of mechanism trading to neuronal cell death caused by Abeta using cultured hippocampal neurons. For this purpose, we measured lactate dehydrogenase (LDH) in the culture media after treatment with Abeta combined with anti-oxidant drug, trolox, or not. By histochemical and TUNEL method, we studied the change of immunoreaction to anti-MAP-2 (microtubule associated protein -2, the main component of neuritis) and detected apoptotic cells, respectively, in the hippocampal neurons treated with Abeta. To investigate whether tau phosphorylation involve neurotoxicity induced by Abeta, we immunostained the neurons with anti-SMI-31 to recognize phosphorylated Ser 396/404 of tau. From our data, we suggested that Abeta1-40 and Abeta25-35 induced marked neurodegenerative changes, and the mechanism responsible for cell death caused by Abeta -neurotoxicity was associated with the apoptosis. Because Abeta-neurotoxicity was not inhibited by anti-oxidant, trolox, we suggested that anti-oxidant did not protect the neuronal cells against the damage induced by Abeta in ou. expo.imental envi.onment. Finally, we suggested that AP treatment did not potentiate the immunoreactivity to anti-phosphorylated tau antibody and we speculated that Abeta-neurotoxicity led hippocampal cells to apoptosis without tau phosphorylation.