Intraneuronal aggregation of specific hyperphosphorylated tau isoforms in subsets of neurons may explain many neurodegenerative processes. Only some antibodies including AP422 and AT100 are specific to the abnormal phosphorylation of tau proteins in these processes. AT100-immunoreactivity was never observed in cell models with the exception of Sf9 cells. In the present study, we developed a way to induce AT100-immunoreactivity in different cell types including COS and SY5Y cells after tau cDNA transfection and treatment by okadaic acid. This represents a useful model to study abnormal tau phosphorylation in situ.