Abstract: The present invention relates to methods for assessing binding agent specificity, in particular antibody specificity. The present invention thus provides a method of analysing a mixture of polypeptides comprising the steps of: (i) separating the polypeptides in the mixture into a plurality of fractions; (ii) contacting a first aliquot of two or more of the fractions with a plurality of different binding agents attached to one or more solid supports and detecting the binding of the polypeptides to the binding agents in each fraction; (iii) assessing the amino acid composition of the polypeptides in a second aliquot of said fractions by mass spectrometry; and (iv) correlating the binding results detected in step (ii) and the mass spectrometry results from step (iii) to assess the specificity of the binding agents for a polypeptide of interest.