Abstract: Methods are provided for determining the presence or absence of ragged ends in polymeric proteins or protein products, by means of fast atom bombardment and high mass mass spectrometry (preferably high field magnet mass spectrometry). The methods may be modified for locating N- or C-terminal peptide in a polymeric protein or protein product and for assigning disulphide bridges in polymeric protein or protein products. The methods are applicable to other biopolymers such as nucleotides and carbohydrates.