Sigma′s FLAG Immunoprecipitation kit allows a rapid and efficient immunoprecipitation and elution of an active FLAG-tagged protein. The immunoprecipitation is performed with the ANTI-FLAG M2 affinity gel, which is a highly specific monoclonal antibody covalently attached to agarose resin. The use of affinity resin allows an efficient binding of FLAG-tagged proteins without the need for preliminary steps and calibrations. The immunoprecipitated FLAG-tagged proteins can be efficiently eluted from the resin with acidic conditions or by competition with FLAG peptide. The immunoprecipitated proteins can be detected for their size, post-translational modifications, and interactions on gel electrophoresis, and by activity assays.