Amyloid deposits derived from the amylin peptide accumulate within pancreatic islet β-cells in most cases of type-2 diabetes mellitus (T2Dm). Human amylin ‘oligomers’ are toxic to these cells. Using two different experimental techniques, we found that H₂O₂ was generated during the aggregation of human amylin into amyloid fibrils. This process was greatly stimulated by Cu(II) ions, and human amylin was retained on a copper affinity column. In contrast, rodent amylin, which is not toxic, failed to generate any H₂O₂ and did not interact with copper. We conclude that the formation of H₂O₂ from amylin could contribute to the progressive degeneration of islet cells in T2Dm.