Tota1114 patients were studied prospectively with radioiodine uptake (RAIU) and 'TcO, thyroid scan to design a very simpte, rapid and inexpensive method measuring the thyroid uptake on thyroid scan. After the RAIU was obtained at 24 hours after P.O. of "'I, Thyroid scan was perforrned at 20 minutes after I.V. of " Tc04 and the bilateral salivary glands were included in the scan field. Pinhole collimated and computer assisted gamma camera was used. Three regions of interest were set on each salivary gland and on the thyroid by automatic edge detection method. Mean counts per pixel were calculated for each ROI and the salivary-thyroid rativ(STR) was defined as; STR (%)= Mean counts per pixel of salivary glands (KC)/Mean counts per pixel of thyroid gland (KC)*100 114 cases consisted of 41 normal, 55 hyperthyroid and 18 hypothyroid patients and correlation between the STR and the RAIU were evaluated in total and each group. The STR and the RAIV showed reverse linear regression in 114 cases (r=-0.8, P=O) and closer correlation was showed in hyperthyroid group (r=-0.9, P=0). Mean STR in normal group was 47.6%. In predicting the RAIU by STR, sensitivity and specificity were 88.3% and 64.9% in 114 cases and 95.3% and 83.3% in hyperthyroid group. It is recommended that the STR be used in place of the RAIU giving same information at saving time, money and radiation exposure.