Human α-synuclein was originally identified as the precursor of a peptide named non-Aβ component of Alzheimer’s disease (NAC) that was tightly associated to purified Alzheimer’s disease amyloid (1). Senile amyloid plaques consist predominantly of the 39-42 amino acid residue peptide Aβ arranged in β-pleated sheets. Aβ is generated by hydrolysis from the transmembrane amyloid precursor protein APP. The mechanism by which the intracellular presynaptic α-synuclein or its NAC fragment becomes integrated in extracellular senile plaques is still unclear. However, in vitro studies have shown that NAC and α-synuclein have the potential to participate actively in the biology of senile plaques since NAC can (1) interact with Aβ (2), (2) form amyloid fibrils (3), and (3) stimulate the aggregation of Aβ (4). α-synuclein can also stimulate Aβ aggregation and interact with senile plaques in situ (5). The techniques described in this chapter allow the study of interactions of α-synuclein with senile plaques in brain sections and with Aβ peptides in solution. Information on the following points are found in Jensen et al. (5) and references therein: (1) Expression and purification of recombinant human α-synuclein; (2) methodology for performing sodium dodecyl sulfate (SDS) gel electrophoresis and fluorography; and (3) standard histologic techniques for fixing, sectioning, and handling of human brain tissue.