The author observed the uptake rate 131I by the thyroid gland and disappearing rate of the 131I at the size of the intradermal injection of 0.1ml of 5mCi of 131I in normal physiologic saline on 20 patients with hyperthyroidism and on 15 patients with hypothyroidism who visited the Radioisotope department of the Pusan National University Hospital during the period from January 1967 to Aug. 1968 and during the same period 15 normal persons were examined by the same methods and found. The results were as follows:(1) The disappearance of rate of 131I at the injected site was highest in the cases of hyperthyroidism. The next highest results were obtained in the normal cases. The lowest results were obtained in the cases of hypothyroidism. (2) The uptake rate of thyroid gland after intradermal injection of the 131I was highest in the cases of hyperthyroidism and the next highest results were obtained in the cases of normal findings. The lowest results were obtained in the cases of hypothyroidism. (3) In conclusion, the intradermal method of injecting 131I by the author is a useful way of testing the function of the thyroid gland.