Background: Salivary flow rate (SFR), to estimate salivary gland dysfunction and radioactivity in different body fluids, to evaluate its intensity, were determined in thyroid patients after 131-I therapy. Material and Methods: For determination of SFR an innovative sponge test was adopted and the radioactivity in saliva, blood and serum of thyroid patients was determined by NaI (TI) Scintillation Radiation Detector. Results: There was a significant reduction in SFR at 2 weeks after RAIT. At 3 hours after administration of 555−1073 MBq to the benign thyroid patients, the radioactivity in 1 g of saliva, 2.5 mL of blood and 0.6 mL of serum was 17.24, 0.74 and 0.25 MBq respectively. In the same patients, at 2 weeks after RAIT, the radioactivity was decreased and was found to be 0.22, 0.13 and 0.09 MBq in saliva, blood and serum respectively. In malignant thyroid patients treated with 3700−9250 MBq, the radioactivity at 3 hours after RAIT in the studied samples of saliva, blood and serum was 200.72, 9.14 and 3.07 MBq and at 2 weeks after RAIT, radioactivity in samples was decreased up to 0.15, 0.05 and 0.03 MBq respectively. Conclusions: An indigenously designed sponge test was simple, safe and quick method to determine the SFR. The sudden increase of radioactivity was found in all studied samples within 3 hours after RAIT and reduced significantly at 2 weeks after RAIT. The raised radioactivity at 3 hours after RAIT was sufficient to impart its harmful effects even to all interactive persons.