Use of heteropoly acids as immunological precipitin brighteners

Aqueous solutions of the heteropoly acids, phosphotungstic and phosphomolybdic, are excellent precipitin brighteners for analytical immunological reactions such as radial immunodiffusion and electroimmunodiffusion in agarose gel media. These substances not only enhance the immunoprecipitate, enabling distinct differentiation from background residual protein, but also enable subsequent removal of residual nonimmunoprecipitated protein by saline solution prior to staining.