Human influenza hemagglutinin (HA) is a surface glycoprotein required for the infectivity of the human virus. The HA tag is derived from the HA protein has been e, Xenopus/Amphibian,tensively used as a general epitope tag in e, Xenopus/Amphibian,pression vectors. Many recombinant proteins have been engineered to e, Xenopus/Amphibian,press the HA tag, which does not appear to interfere with the bioactivity or the biodistribution of the recombinant protein. This tag facilitates the detection, isolation, and purification of the proteins.