Abstract
Iodinated compounds which appear in the serum after administration of a therapeutic dose of I131 for hyderthyroidism or thyroid cancer were isolated by chromatographic fractionations. The relationships between the time of appearance of these compounds, the response of the patients, the amount of radiation to the thyroid and the rate of disappearance of radioactivity from the gland were discussed. Triiodothyronine was detected in the serum in 19 patients, monoiodotyrosine in 14 and diiodotyrosine in 6. Evidence is presented to suggest that the presence of triiodothyronine is related to the degree of thyrotoxicosis and not to the effect of irradiation. The presence of diiodotyrosine appeared to be the result of radiation damage to the thyroid.