Alzheimer’s disease (AD) is the most common cause of late-life dementia (Wisniewski and Frangione, 1996). AD can be divided into an early-onset form (onset 60 years) and the more common late-onset (60 years) form. So far, three genes have been linked to earlyonset AD including the ß-amyloid precursor protein (ßPP) on chromosome 21 (Levy et al., 1990; Goate et al., 1991), presenilin 1 (PS1) on chromosome 14 (Schellenberg, 1992; Sherrington et al., 1995), and presenilin 2 on chromosome 1 (PS2)(Levy-Lahad et al., 1995; Rogaev et al., 1995; Li et al., 1995). The majority of early-onset AD is thought to be related to mutations in PS1 and 2, while for late-onset AD an association with the inheritance of the apolipoprotein (apo) E allele E4 has been described (Corder et al., 1993; Strittmatter et al., 1993). The presence of the apoE4 allele appears to be predominantly a risk factor for patients with an onset of AD between the ages of 60 and 70 (Blacker et al., 1997). ApoE4 is also a risk factor for the related condition of congophilic angiopathy (Premkumar et al., 1996; Greenberg et al., 1996), as well as multi-infarction dementia (Shimano et al., 1989; Slooter et al., 1997). Neuropathologically, each of these subtypes of AD is characterized by four major lesions:(a) intraneuronal, cytoplasmic deposits of neurofibrillary tangles (NFT);(b) parenchymal amyloid deposits called neuritic plaques;(c) cerebrovascular amyloidosis; and (d) synaptic loss. The major constituent of the neuritic plaques and congophilic angiopathy is amyloid ß (Aß), although these deposits also contain other proteins (Wisniewski & Frangione, 1996). The amyloid deposits in AD share a number of properties with all the other cerebral amyloidoses such as the prion-related amyloidoses, as well as the systemic amyloidoses. These characteristics are:(1) being relatively insoluble;(2) having a high ß-sheet secondary structure, which is associated with a tendency to aggregate or polymerize;(3) ultrastructurally the deposits are mainly fibrillary;(4) the presence of certain amyloid-associated proteins such as amyloid P component, proteoglycans, and apolipoproteins;(5) the deposits show a characteristic apple-green birifringence when viewed under polarized light, after Congo red staining. All of the proteins with linkage to AD have now been found as components of neuritic plaques (Masters et al., 1985; Wisniewski et al., 1995b, c). It remains to be determined whether all these proteins are involved in the same or different pathological pathways and which of these proteins is the most important for the most common, late-onset form of AD.