The presence of salts and metal cations in and '^^I-sodium iodide solutions separated from ^^''^Te targets promotes autoradiolytic decomposition of iodide to several different iodine species dependent upon the chemical environment. The stabilization of the radioiodine as iodide by removal of trace salts and trace metal cations and in the absence of reducing agents is described. The high specific activity and '^"'I-iodide is suitable for labeling antibodies, proteins and radiopharmaceuticals.