Novel peptides are disclosed that may be used as inhibitors of amyloidogenesis, as suppressors of amyloid toxicity, and as therapeutic agents for amyloid-associated diseases such as Alzheimer's disease, Parkinson's Disease, Creutzfeldt-Jakob Disease, Huntington's Disease, and Type II Diabetes. These new .beta.-strand mimics (.beta.-sheet "blockers"), containing C.sup..alpha.,.alpha.-disubstituted amino acids, specifically interact with and block the development of the .beta.-sheet structure of the developing fibrils of amyloid diseases, such as Alzheimer's disease amyloid .beta.-peptide (A.beta.). We have discovered that oligomerization of .beta.-sheet structures, including those implicated in amyloid-associated diseases, may be inhibited or even reversed by the presence of extended peptide structures that have only one edge available for hydrogen bonding. Without a second edge that is also available for hydrogen bonding, the extension of a developing .beta.-sheet is blocked by binding to the novel peptides.