Alzheimer's disease is a fatal neurodegenerative disorder involving the abnormal accumulation and deposition of peptides (amyloid-beta, A beta) derived from the amyloid precursor protein. Here, we present the structure and the Zn2+ binding sites of human and rat A beta(1 -28) fragments in water/sodium dodecyl sulfate (SDS) micelles by using H-1 NMR spectroscopy. The chemical shift variations measured after Zn2+ addition at T > 310 K allowed us to assign the binding donor atoms in both rat and human zinc complexes. The Asp-1 amine, His-6 N delta, Glu-11 COO-, and His-13 N epsilon of rat A beta(28) all enter the metal coordination sphere, while His-6 N delta, His-13, His-14 N epsilon, Asp-1 amine, and/or Glu-11 COO- are all bound to Zn2+ in the case of human A beta(28). Finally, a comparison between the rat and human binding abilities was discussed.