Amyloid plaques, invariantly associated with Alzheimer’s disease (AD), contain amyloid β-protein (Aβ) as the primary protein component. 1 The 39-43 amino acid Aβ is derived from the β-amyloid precursor protein (APP), an integral membrane protein of unknown function. 2 Recent findings particularly implicate the more hydrophobic and highly insoluble 42 amino acid variant (Aβ42) in amyloid plaque formation and in the pathogenesis of AD. 3-5 Although Aβ42 accounts for only about 10% of total Aβ secreted from cells (roughly 90% is the 40 amino acid variant Aβ40), Aβ42 is the major protein component of the diffuse, largely nonfibrillar plaques which precede the development of the dense, fibrillar neuritic plaques characteristic of AD. 6, 7 Genetic evidence strongly implicates Aβ in general and Aβ42 in particular in the etiology of AD: all mutations linked to familial early-onset AD (FAD) examined to date result in increased production of Aβ42 or of both Aβ40 and