The B Tag is a hexapeptide epitope with the sequence, QYPALT, derived from the major core protein VP7 of the Bluetongue virus (BTV). In addition to its small size, it features a sequence comprised entirely of uncharged amino acids. It can be fused to the N- or C- ends, as well as in the middle of fusion proteins. Antibodies to the B epitope may serve as useful tools in the immunological detection or purification of B-tagged proteins.