Hyperphosphorylation of the microtubule-associated tau proteins is one of the main pathological events that leads to neurofibrillary neurodegeneration in Alzheimer's disease. A similar tau phosphorylation pattern may be obtained in SY-5Y neuroblastoma cells after okadaic acid treatment. In this paper, we clearly demonstrate phosphorylation of Ser422 in tau proteins of treated cells as well as in Alzheimer brain homogenates. By contrast, Ser422 was not phosphorylated on native tau proteins from non-treated cells or rapidly processed biopsies. These results confirm that this cell model is still relevant to study neurofibrillary neurodegeneration of the Alzheimer type.