Rotational resonance (R(2)) solid-state NMR spectroscopy was used to measure six intercarbon distances in amyloid fibrils comprising C-13-labeled analogs of a peptide (AcHN-SNNFGAILSS-CONH2, IAPP(H)(20-29)) based on residues 20-29 of the human islet amyloid polypeptide (amylin, IAPP(H)). The intramolecular intercarbon distances, which constrain the peptide backbone dihedral angles (phi, psi), suggest that IAPP(H)(20-29) adopts a highly pleated beta sheet structure in the amyloid fibril. This structure is more compact than the antiparallel beta sheet model formulated by Pauling to describe the silk fibril. Exaggerated pleating may allow intrastrand van der Waals interactions between hydrophobic side chains. Interstrand interactions can be modeled using qualitative intermolecular R(2) effects which are observed in label dilution experiments. An intermolecular R(2) effect was observed between the C-alpha of Ala25 and the C=O of Ile26, suggesting their proximity in the amyloid beta sheet. The R(2) SSNMR measurements allow the refinement of our two-dimensional model of the IAPP(H)(20-29) amyloid beta sheet. The refined model may facilitate the design of molecules that bind to pancreatic amyloid. Such molecules may be useful as diagnostics or therapeutics for type-II diabetes.