The 20-minute Tc-99m-pertechnetate uptake became readily available for routine use and it replaced 131I for thyroid imaging. However measuring thyroid uptake during a 5-minute minimizes pertechnetate uptake by the salivary glands and presence of contaminated saliva from those glands in to the pharynx and esophagus. A study was carried out to determine the suitability of the utility of a 5-minute and 20-minute interval from administration of Tc-99m-pertechnetate to imaging and uptake measurement as a replacement for the 24 hour standard originally established with 131I, and to evaluate the relationship between 5-minute Tc-99m-pertechnetate uptake and other thyroid functions. A 5-minute and 20-minute uptake of Tc-99m-pertechnetate were measured in 70 patients with thyroid disease at Yeungnam University Hospital from March 1, 1991 to Feb. 29, 1992. The results were as follows. 1) The 5-minute Tc-99m-pertechnetate uptake in Graves' disease, Hashimoto's thyroiditis, simple goiter non toxic nodular goiter, subacute thyroiditis and euthyroid were 18.2%, 14.6%, 2.8%, 3.2%, 1.2% and 1.1%, respectively. There was a significant difference between the mean of the euthyroid group and the mean of the Graves' disease. So differenciation between them can be easily made. 2) The 5 minute Tc-99m- pertechnetate thyroid uptake was well correlated with 24 hour 131I thyroid uptake (r=0.75, p〈0.001). These data provided an equation for estimating the 24 hour uptake of iodide given the 5 minute pertechnetate uptake: Estimated 24-hour 131I thyroid Uptake = 7.188*ln (5 minute Tc-99m- Pertechnetate uptake)+16.94 3) The 20-minute Tc-99m-pertechnetate thyroid uptake was well correlated with 24-hour 131I uptake (r=0.72, p〈0.001) and 5-minute Tc-99m-pertechnetate thyroid uptake (r=0.96, p〈0.001). 4) In the Graves' disease, The 5-minute Tc-99m-pertechnetate thyroid uptake was well correlated with serum T3-resin uptake (r=0.46, p〈0.01), serum total T3 (r=0.55, p〈0.05), serum total T4 (r=0.46, p〈0.05). These results suggest that 5-minute Tc-99m- pertechnetate thyroid uptake has been found at least as useful as 24-hour 131I uptake for diagnostic confirmation at our hosptial, the logistical advantages of completing the diagnosis. The exam in 5-minutes led us to abandon the 24-hour study in the majority of patients, but the 24-hour 131I uptake is still obtained in patients with planned or potential radioiodine therapy.