This proposal combines small-angle neutron scattering with novel labelling strategies to investigate “amyloid” protein fibrils. Variations in packing and in the dynamics of elongation and breakage underpin phenomena ranging from non-genetic heredity in yeast, to diseases such as Alzheimer’s, BSE and CJD. Most solution methods to monitor growth dynamics only give information on the overall % of material transformed from non-fibrillar to fibrillar forms. They cannot determine length distribution or linear growth rates, but instead convolute the two; in other words, they cannot distinguish a few long fibrils each growing quickly, from many short fibrils each growing more slowly. We will determine both fibril lengths and linear growth rates using a novel SANS approach with labelled ends growing on contrast-matched "seed" fibrils