By using 99m Tc-Pertechnetate, we evaluated the thyroid function of 136 persons with uptake slopeindex(U.S.I.) which was calculated by computerized dynamic flow study. Also, we compared our results of U.S.I.with those of established 131 I-24 hr uptake % in given materials by comparative analysis of their correlationwith the hormonal values of T3, T4, Free T4. The results wre as follows: 1. The U.S.I. of euthyroidismal group andhyperthyrodismal group were 4.87±2.26, 27.67±9.56 respectively. The 131 I-24 hr uptake % of above groups were29.22±10.23, and 71.45±15.51. So the differentiation of the two groups could be done more easily by using99mTc-Pertenchnetate U.S.I. than by using 131 I-24 hr uptake %. 2. The correlation rates between 99mTc-Pertechnetate U.S.I. and other laboratory hormon levels, T3, T4, Free T4, ar almost parallel with thosebetweeen 131 I-24 hr uptake % and the values of T3, T4, Free T4. Also the direct correlation rate between 99mTc-Pertechnetate U.S.I. and 131 I-24 hr uptake % was 0.898. So, the method of thyroidal function evaluation by 99mTc-Pettechnetate U.S.I. is very reliable. 3. The 99m Tc-Pertechnetate U.S.I. is very helpful to evaulate thefunctions of each lobe respectively incases 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 withoutpreparation and especially helpful in debilitating patient and patients under antithyroid drug therapy, who needrepetitive follow-up examination.