By using 99mTc-Pertechnetate, we evaluated the thyroid function of 136 persons with uptake slope index (U.S.I) which was calculated by computterized dynamic flow study. Also, we compared our result of U.S.I with those of established 1311-24 hr uptake% in given materials by comparative analysis of their correlation with the hormonal values of T3, T4, Free T4. The results were as follows: 1. The U.S.I of euthyroidismal group and hyperthyrodismal group were 4.87$pm$2.26, 27.67$pm$9.56 respectively. The 1311-24 hr uptake% of above groups were 29.22$pm$10.23, and 71.45$pm$15.51 So the differentiation of the two groups could be done more easily by using 99mTc-Pertechnetate U.S.I than by using 1311-24 hr uptake %. 2. The correlation rates between 99mTc-Pertechnetate U.S.I and other laboratory hormon levels, T3, T4, Free T4, are almost parallel with those between 1311-24 hr uptake % and the values of T3, T4, Free T4, Also the direct correlation rate between 99mTc-Pertechnetate U.S.I, and 1311-24 hr uptake % was 0.898 So, the method of thyroidal function evaluation by 99mTc-Pertechnetate U.S.I isvery reliable. 3. The 99mTc-Pertechnetate U.S.I is very helpful to evaulate the functions of each lobe respectively in cases of having obviously different radioactivity between both lobes. 4. 99mTc-Pertechnetate used dynamic thyroid function study and scan can be performed during the short time without preparation and especially helpful in debilitating patient and patients and patients under antithyroid drug therapy, who need repetitive follow-up examination.