Aβ (12-28) represents a binding site for apolipoprotein E (apoE). ApoE is a genetically inherited risk factor for Alzheimer’s disease that promotes aggregation of toxic Aβ. This sequence encompasses a hydrophobic domain (residues 14–21) and a ß-turn (residues 22–28) which place two hydrophobic domains of Aß 14 to 21 and 29 to 40/42 opposite each other, allowing for the assembly of Aß peptides into fibrils. The secondary structure of Aß (12- 28), a neutral peptide, is dominated by a-helix and random coil. The interaction of apoE with residues 12 to 28 of Aß is not just a non-specific hydrophobic interaction but plays a pivotal role in the mechanism of Aß pathology in Alzheimer’s disease (AD). Aß (11-28) and five other fragments enhanced aggregation of full length Aß (1-40). All of the peptides that enhance aggregation contained either residues 17 to 20 or 30 to 35, indicating the importance of these regions for promoting aggregation of full-length Aß.