The thyroid uptake study of 131I that has been most commonly used in the diagnosis of the thyroid disease, is usually performed by giving oral administration in fasting state. Therefore, the patients with thyroid disease have to visit the hospital in fasting state and on two sucessive days for this uptake study of the thyroid gland. This study was included the total number of 87 cases: Of these, radioiodine was orally administered to 8 healthy individuals, 46 cases that were euthyroid received it intravenously, and 33 patients with hyperthyroidism, it was also administered intravenously. All of the cases uptake rates by thyroid gland were measured at the time of 15min, 30min, 1, 2, 6 and 24 hours after administration of 131I. In an attempt to minimize such an inconvenience for the patients as well as shorten the time of examination, the authors have made an observation on early uptake rates by thyroid gland and changes of thyroid function as related to the meals. The result btained are summerized as follow: 1. In both cases of oral and I.V. administration, there were found higher tendencies of uptake rate in non-fasting state than in fasting state, oral administration stastically showed definite significance of increasing uptake rate in non-fasting state after 6 hours while I.V. administration showed this after one hour. 2. When 131Iwas administered intravenously the early thyroid uptake rate showed higer tendencies than oral administration, that is, if the values of uptake rate surpass 20% after one hour measurement, hyperthyroidism could be highly suspected and if exceeds 40% of 6 hour uptake rate, hyperthyroidism may certainly be predicted to exist. 3. The uptake rate of non-fasting state I somewhat higher than in fasting state, however, since the differences exist only with the negligerble boundary, the test of non-fasting state is considered to have a good validity. 4. Finally it was felt that euthyroidism and hyperthyrodism could be differentiate within 6 hours after intravenous injection in an usual non-fasting state, and results not only in an increase in rapidity of the diagnosis but also more convenience with a great saving in time.