t. irradiation observations anc the many physiological and histological on tissue tO appraise the resuits. studies to be made With experience, it. was discovefred that the neoplas not only appeared frequently but resulted with a high degree of preflictability, if the actual uptake and retention of 131) was known and the long period a f post radiation observed. This predictability has provided a means for watching the development of neoplasms from their inception to large destructive growths in the radiated thyroid without the use of thyroid stimulating substances. The various techniques of radioautography, developed or modif ed in our laboratory, using 131, in the humans at the time of an operation and 131, and tritiated thy- midine (7H-TaR) in the rats have provided important information on the physiological function and mitotic activity as a neoplasm developed. Many of th se observations anc the techniques used to study tissues lead to the studies on the Ma rShallese who we hav operated. The detailed biochemical studies on individuals treated with radioiodine also lead to important contributions to kenetic data on some patie tts in the National Thyrotoxicosis Follow-Up Study with which we have a major part. These studies have lead to the collaboration with numerous other groups with Similar or collateral interests: Dr. A.B. Brill (formerly Vanderthit, now of Brook- haven National Laboratory) for analysis of 9 compartment iodine kifmetics; Dr. P. Reec Larson (Harvard) for refinement of our rat TSH assay; Dr. Hunter eath (Mayo Clinic) for rat calcitonin assays; Dr. Robert Conard (Brookhaven National Laboratory) in the Study of Marshallese; Dr. E.D. Williams (Cardiff) for identificatgon of C-cell neoplz Objectives The objectives of the research in clinical subjects were: L. To obtain precise detailed data on the amount and behavior o 131; radiation delivered to the thyroid for reference to the subsequent observat fons on that thyroi