THE EARLY studies with radioactive iodine by Hertz, Roberts, and Evans1 and by Hamilton and Soley,2 in which it was demonstrated that the natural avidity of the thyroid for iodine could be used to selectively deposit radioactive isotopes of iodine in thyroid tissues, led to the hopeful hypothesis that diseased thyroid tissue might be effectively irradiated by administering radioactive iodine to patients suffering with such maladies. Already it has been amply demonstrated in many clinics that exophthalmic goiter (Graves's disease) can be successfully treated with radioactive iodine. Indeed, the complete replacement of surgical and other forms of treatment by radioiodine is delayed only by an uncertainty as to its possible subsequent undesirable effects on the remaining thyroid tissue. In following the above hopeful hypothesis, a group of investigators at Presbyterian Hospital and Columbia University reported the first attempts to localize radioactive iodine in cancers of the thyroid in