Radioactive iodine (¹²⁵I) is routinely used by researchers to label proteins. The iodination of proteins can be performed enzymatically or chemically. The Bolton-Hunter reagent is designed to aid the labeling of proteins with radioactive iodine.

The Bolton-Hunter reagent is used to add tyrosine-like groups to end-terminal α-amino groups or ε-amino groups of lysine that result in increased protein iodination.