Alzheimer’s disease (AD) is associated with plaque deposition in the brain of AD patients. The major component of the aggregate is a 39–42 long peptide termed β-amyloid (Aβ). Except for Aβ, plaques contain several other components which co-precipitate together with Aβ. One such component is the small heat shock protein (sHSP) αB-crystallin. Instead of preventing the cell from the neurotoxicity of Aβ, αB-crystallin induces an increased neurotoxicity.We find – using solution state NMR spectroscopy – that αB-crystallin competes efficiently for Aβ monomer–monomer interactions. Interactions between Aβ and αB-crystallin involve the hydrophobic core residues 17–21 as well as residues 31–32 of Aβ, and thus the same chemical groups which are important for Aβ aggregation. In the presence of αB-crystallin, Met35 in Aβ becomes efficiently oxidized. In order to quantify the redox properties of the different complexes consisting of Aβ/αB-crystallin/copper, we suggest an NMR assay which allows to estimate the electrochemical properties indirectly by monitoring the rate of glutathion (GSH) auto-oxidation. The oxidation of the side chain Met35 in Aβ might account for the increased neurotoxicity and the inability of Aβ to form fibrillar structures, which has been observed previously in the presence of αB-crystallin [Stege, G.J. et al. (1999) The molecular chaperone αB-crystallin enhances amyloid-beta neurotoxicity. Biochem. Biophys. Res. Commun. 262, 152–156.].