For several years peptides have been used to investigate many aspects of the molecular mechanisms supporting the etiopathogenesis of neurological diseases. Even if well-established and commercially-available assays for the diagnosis of neurological diseases, based on peptides, are presently not available, much research has been focused to the comprehension of the pathogenetic mechanisms of relevant neurological diseases, such as Multiple Sclerosis, Alzheimer's disease and prion diseases. Several peptides, which strongly contributed to increase in the progress, and in the understanding of the molecular mechanisms of these important diseases, have been selected as antigens to be proposed in possible alternative diagnostic methodologies. The authors focused their attention on the possible peptides to be used as diagnostics for these three characteristic neurological diseases. In fact, Multiple Sclerosis is an autoimmune disease in which peptides have been used for the characterization of both B and T immune response, while Alzheimer's disease and prion diseases can be cumulative regarded as "protein folding disorders" in which peptides can be used to identify the misfolded protein.