Amyloid deposits derived from the amylin peptide accumulate within pancreatic islet P-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 H202 from amylin could contribute to the progressive degeneration of islet cells in T213m. (c) 2007 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.