Alzheimer's disease (AD) is a progressive neurodegenerative disorder. Pathology visible "post mortem" includes neurodegeneration and extracellular deposition of amyloids, both in neuritic plaques and diffuse deposits. [1] The major proteinaceous component of AD amyloids is the amyloid-b protein (Ab), a protein consisting of 39-42 amino acids derived from the Alzheimer precursor protein (APP). [2] Inhibition of the formation of b-amyloid fibrils, formed by self assembly from this amyloid b-peptide is an attractive target for the treatment of Alzheimer's disease. [3] In the last few years, various small molecules such as rifampicin, Congo red, curcumin, and apomorphin have been shown to inhibit Ab aggregation both in vitro and in cell assays. [4] Besides these molecules, which are rather unspecific and whose mode of action is completely unclear, only very few examples of designed b-sheet breakers are known so far. [5] These are mainly oligopeptides, representing fragments of Ab itself. For example, Kiessling used Tjernbergs' [5g] oligopeptide KLVFF, which is based on one of the selfassembling recognition sequences of the amyloid peptide (residues 16-20) and added positively charged lysines to enhance the solubility of the aggregates. [5e,j] Soto's pentapeptide amides were also based on the KLVFF recognition sequence of Ab. [5h,i] HetØnyi showed that the cationic pentapeptide amide RVVIA, which is based on the C-terminal sequence VVIA of Ab (1-42), also interferes with fibril formation. [5c,d,f] All these oligopeptides require millimolar concentrations and an up to 20fold excess relative to Ab (1-42) to reduce the amount of fibrils by 40 % at best. Unfortunately, very little is known about their mechanism of action, their exact binding specifities or the mo- [a]