Amyloid peptides (Abeta) play a central role in the pathogenesis of Alzheimer's disease (AD). The aggregation of Abeta molecules leads to fibril and plaque formation. Fibrillogenesis is at the same time a marker and an indirect cause of AD. Inhibition of the aggregation of Abeta could be a realistic therapy for the illness. Beta sheet breakers (BSBs) are one type of fibrillogenesis inhibitors. The first BSB peptides were designed by Tjernberg et al. (1996) and Soto et al. (1998). These pentapeptides have proved their efficiency in vitro and in vivo. In the present study, the effects of two pentapeptide amides are reported. These compounds were designed by using the C-terminal sequence of the amyloid peptide as a template. Biological assays were applied to demonstrate efficiency. Modes of action were studied by FT-IR spectroscopy and molecular modeling methods. (C) 2002 Elsevier Science (USA).