The sequence of this peptide is derived from the hydrophobic core of Aß 40, (Aß16-20). This hydrophobic analog possesses alternating N-methyl amino acids and is highly water soluble considering Ac-KLVFF-NH2 without N-methylation is only sparingly soluble. This cell permeable peptide not only inhibits fibril formation, it also disrupts preformed fibrils. It is able to pass spontaneously through both synthetic phospholipid bilayer vesicles and cell membranes.