Electrophoretic migration shift assay shows that human neuronal tau can bind to λDNA, plasmid DNA and DNA fragment of PCR product from human cDNA. One mole of neuronal tau binds to a fragment of 6～10 bp nucleotides. Under atomic force microscope, a necklace complex of tau-DNA has been directly observed. Experiments in immunohistochemistry with a monoclonal antibody Tau-1 exhibit condense nuclear staining of tau as well as diffuse cytoplasmic staining of tau. It suggests that neuronal tau plays an important role in nucleus.