Abstract: This invention provides a method of identifying or characterising an immune response in a subject comprising: (a) contacting a sample containing immunoglobulins from the subject with at least one antigen immobilised on a support; (b) washing unbound, non-antigen specific immunoglobulins from the support to leave antigen-specific immunoglobulins bound to the antigen on the support; (c) optionally eluting the antigen-specific immunoglobulins from the antigen on the support; and (d) subjecting the antigen-specific immunoglobulins to mass spectrometry to identify two or more different antigen specific immunoglobulin classes, subclasses and/or light chain types.