3x DYKDDDDK peptide, also called 3x FLAG peptide, is a 23 aa length peptide used for the competitive elution of DYKDDDDK-tag fusion proteins (with excess of free 3x DYKDDDDK peptide) under non-denaturing conditions, especially when a DYKDDDDK-tagged protein is sensitive to low pH. This peptide includs an enterokinase-cleavage site, was specifically designed for immunoaffinity chromatography.