Epitope tagging is a powerful and versatile strategy for detecting and purifying proteins expressed by cloned genes. Short sequences encoding the epitope tag are cloned in-frame with target DNA to produce fusion proteins containing the epitope tag peptide. Due to their small size, epitope tags do not affect the tagged protein’s biochemical properties. Anti-epitope tag antibodies can serve as universal purification or detection reagents for any tag-containing protein. The DDDDK epitope tag peptide sequence (DYKDDDDK) was first derived from the 11-amino-acid leader peptide of the gene-10 product from bacteriophage T7. The DDDDK peptide has been widely used as a multi-purpose tag, and anti-DDDDK antibodies are optimally suited for identifying, detecting, purifying, and monitoring the expression levels of recombinant DDDDK fusion proteins.