The mechanism of amyloid peptide formation in normally functioning neuron and upon the development of amyloidosis resulting in neuronal death is described. Amyloid peptides are formed by enzymatic processing of a large protein precursor and participate in intermolecular interactions after conformational rearrangements resulting in the formation of pathogenic structures. They enter into the cascade of molecular and cellular events leading to amyloidosis and death of neuronal cells. These molecular events clarify the relation between the conformation and function of neuropathogenic peptides and the role of this relation in the development of pathology of differentiated neurons.