We describe methods for identifying aggregation-prone regions in structured—that is folded—proteins. Embodiments of the method use a local propensity for aggregation (Ai) at an amino acid position, this being determined by a combination of a hydrophobicity value, an α-helix propensity value, a β-sheet propensity value, a charge value and a pattern value for the amino acid position. This is combined with local structural stability values for the amino acid positions to identify one or more regions in the amino acid sequence which, in the folded protein, are predicted to promote aggregation.