The pattern of neurofibrillary changes which gradually develops in the course of Alzheimer's disease bears a striking resemblance to the inverse sequence of cortical myelination. Factors released by oligodendrocytes exert a strong influence upon nerve cells and suppress disordered neuritic outgrowth. It is suggested that the lack of such factors due to premature dysfunction of oligodendrocytes leads to alterations of the neuronal cytoskeleton and eventually to the appearance of Alzheimer-type neurofibrillary changes.