Protein MetO is a reversible oxidative modification that occurs by exposure of protein(s) methionine residues to reactive oxygen species (ROS). Methionine oxidation can alter the function(s) of the modified proteins and if not reversed by MetO reductases can be further oxidized to methionine sulfone, an irreversible modification. Cayman's MetO Immunoblotting Kit contains reagents needed for the immunochemical detection of proteins containing MetO residues by western blotting. MetO-containing samples of interest include those from cell or tissue lysates as well as semi-pure or purified proteins.