Progress in the search for the cause of Alzheimer's disease is considerably hampered by the lack of animal or in vitro model. We have shown that in Alzheimer's disease two pathological variants of Tau proteins, called Tau 64 and Tau 69, are regularly present in neural tissue undergoing neurofibrillary degeneration. Beside their diagnostic value, Tau 64 and Tau 69 might enable such a model to be devised at long last. It now seems possible to investigate for biochemical disorders capable of inducing the emergence of these two Tau proteins in neuron cultures or among transgenic animals. The innumerable pathogenetic tracks of Alzheimer's disease (aluminium, zinc, superoxide dismutase and free radicals, proteases and antiproteases, beta protein A4 precursor, etc.) should then be opened to exploration.