beta-Amyloid peptide (betaA) is a major fibrillar component of neuritic plaques in Alzheimer's disease (AD) brains and is related to the pathogenesis of the disease. In this study, using electron microscopy, we describe herein the results concerning the efficacy of compounds that can dissolve preformed betaA fibrils in vitro. For such a purpose, two hydrosoluble and biocompatible polymers such as polyethylene glycol and poly-L-lysine were used. The poly-L-lysine appears as a potent dissolver of preformed betaA fibrils in vitro. Its efficiency is instantaneous. Poly-L-lysine can be used as a universal dissolver of all types of oligomeric beta-sheet conformation, precursor of the fibrils. This finding provides the basis for future investigation of the therapeutic potential Of poly-L-lysine in terms of preventing and/or retarding amyloidogenesis in AD and other types of amyloid-related disorders. (C) 2002 Elevier Science (USA).