Alzheimer's disease is one of the prevalent forms of human dementia. Its pathology is distinguished by proteinaceous deposits ("amyloid") in the brain. They contain a peptide (beta A4) that is proteolytically derived from a larger transmembrane protein. To follow the different metabolic pathways of this Amyloid Precursor Protein (APP) may thus lead to the elucidation of the molecular basis of Alzheimer's disease. Specific antibodies are necessary tools for this task. Using synthetic peptides, we have characterized the epitope of the APP-specific monoclonal antibody 22C11; it is localized between residues 66 and 81 of APP. Some of the peptides flanking this site exhibited properties generally associated with amyloid, i.e. low solubility, filament formation, and birefringence after Congo Red staining. Exploiting differences in the peptides' aggregational properties, we present evidence that the two dyes Eosin and Direct Red 254, in conjunction with classical amyloid staining by Congo Red, can be used to characterize aggregating, amyloid-like peptides in vitro.