Chromatographically purified rat albumin. Purified rat albumin may be used as a reference antigen, calibrator, coating protein and blocking agent in a variety of immunoassays including immunodiffusion, immunoelectrophoresis, ELISA, Western blotting, dot-immunobinding assays (DIBA), haemagglutination, and cellbinding assays. Not less than 98% as determined by agar-gel electrophoresis, as tested in a concentration of 50 mg/ml at the level of sensitivity of the applied immunoprecipitating techniques.