Amyloid fibrils are characterized by a common structural component, the cross-β spine.Although this core structure was identified some time ago byX-ray diffraction, the detailed arrangement of theβ spine was difficult to determine because of the fibrillar nature of the material.The recently published microcrystal structures of amyloid fibrils from small peptides greatly enhanced our understanding of the atomic-level structure of the amyloid fibril.However, only a few amyloid fibrils can form microcrystals.The dansyl-tryptophan fluorescence resonance energy transfer (FRET) pair was shown to be able to detect the inter-peptide arrangement of the Transthyretin (105-115) amyloid fibril.We combined the known microcrystal structures with the corresponding FRET efficiencies to build a model for amyloid fibril structure classification.