This document specifies a qualitative and quantitative procedure to determine the composition of animal hair fibre blends by LC-MS without protein reduction. The composition of non-animal hair fibres can be measured by ISO 1833- series; then both results are combined to determine the whole composition of fibres. The method is based on a preliminary identification of all fibres in the blend on the basis of their morphology, by light microscopy. In case of fibres of the same animal species are present (e.g. blends of cashmere and mohair), the method is not applicable and the quantitative analysis can be performed using microscopical analysis (e.g. ISO 17751- series).