L5 antibody conjugated to an agarose resin, which can be used for purification of proteins expressing the octapeptide, DYKDDDDK. The DYKDDDDK tag, commonly referred to as Sigma®'s FLAG® Tag, is often used as a protein modification in order to simplify the labeling and detection of proteins. The binding capacity of the L5 agarose resin is greater than 0.8 mg/ml. The resin can be re-used for at least five times. This affinity gel is also useful for immunoprecipitation of DYKDDDDK-tagged protein.