The thyroid uptake study of Ihas been most commonly employed for the purpose of evaluating thyroid function, and 24-hour uptake rate of Iby the thyroid gland is usually regarded as a most valuable single measurement. However, most of the patients with thyroid diseases are evaluated at first as an ut-patient, and therefore, those patients frequently have to visit the radioisotope laboratory several times and on 2 successive days in order to undergo the uptake study of the thyroid gland. In an attempt to minimize such an inconvenience for the patient as well as to shorten the time of examination, the authors have made an observation on the 20-minute uptake curve of Iby the thyroid gland in addition to the usual thyroid uptake rate of Iat 1, 2, 6 and 24 hours following oral administration of 50 $mu$Ci of Na Iin 26 cases of euthyroidism, 15 cases of hyperthyroidism and 10 cases of hypothyroidism. The results obtained are summarized as follows: 1. It was felt that euthyroidism a d hyperthyroidism could be differentiated by 1 and 6 hour uptake of Iby the thyroid gland. When the one and six hour thyroid uptake rates of Iexceed 15% and 30% respectively, hyperthyroidism may certainly be predicted to exist. 2. The early uptake curve of the thyrogram obtained immediately after giving an oral dose of Irevealed definite and steep elevation after lapse of 10 minutes, and the inclinication of this increasing uptake curve reflected well the functional status of the thyroid gland. The mean inclinations of the uptake curves were 29.5$pm$8.3。 in euthyroidism, 45.7$pm$8.4。 in hyperthyroidism and 3.5$pm$3.4。 in hypothyroidism. The difference between those groups was statistically significant. If the inclinication of the uptake curve exceeds 40。, hyperthyroidism may be anticipated, while it can be predicted that hypothyroidism may be present when the inclinication of the uptake curve measures less than 10。.