Many protein-free media have been deveoped, because protein-free media are usually more economical than serum-free. or serum-containing media and facilitate the purification of bioactive materials, We evaluated various iron salts and chelating agents replacing transferrin to develop a protein-free medium for a human-human hybridoma, HB4C5, and found out that ferric citrate,vas favorable for the production and the productivity of monoclonal antibodies.