The usefulness of radioactive isotopes of iodine in the study of iodine metabolism has been demonstrated by several groups of workers.1 They are of particular value in measuring the gross iodine metabolism of the thyroid in situlb in normal persons and in patients whose thyroids need not be removed surgically. The studies reported in this paper, which were carried out with the cooperation of the department of pediatrics of the University of California Medical School, show that by the use of radioactive iodine certain aspects of the iodine metabolism in children with hypothyroidism can be examined.
Ordinary, or stable, iodine and radioactive iodine are chemically and physiologically the same as long as the amount of radioiodine is less than that which produces physiologic changes by the action of its radiation. In these experiments, less than one-fiftieth the amount of radioiodine necessary to produce biologic changes was used. The