This protocol describes a simple chemical oxidation method for labeling antibodies with iodine. Iodide-125 (supplied as NaI) is oxidized to form iodine-125 (I2), which attacks tyrosyl and histidyl side chains. The iodinated antibodies are easily detected and quantitated using gamma counters or film. They are used primarily in immunoassays, but other techniques can be adapted conveniently to the iodine detection method. - [Read Labeling Antibodies with Iodine Protocol]