The application of qualitative immunochemical protein measurements is limited by the lack of available antisera for all species, although this situation is improving. Antisera against human proteins are often useful for closely related species, and some phylogenetically distant species have similar epitopes on their corresponding proteins which allows protein measurements in these species. Some protein require species-specific antisera,e.g. CRP. Where a suitable antiserum is available, it is still necessary to test that the concenter=rations of the antiserum and antigen are appropriate: incorrect reagents may lead to over- or underestimation for the protein under eXamination