I131 Clearance test were performed in 6 different groups of patients.(1)There was hypofunction of the parotid gland in 14 cases of Xerostomia in a narrow sense.Sialogram on 12 of these cases revealed that hypofunction was due to extra-glandular factors in .3 cases, and intra-glandular factors in 6 cases.(2)Examinations of 9 cases of acute parotitis revealed marked decrease or disapperance of the glandular function in all the cases.In chronic parotitis, hypofunction of the gland was not always demonstrated.It seemed like that function of the gland was depended upon the function of the unaffected portion of the gland.(3)The glandular function was within normal limits in 8 cases of mixed tumour of the parotid gland and 3 cases of Mikulicz's disease.There was marked hypofunction of the gland in 2 cases of granuloma and lymphogranuloma.(4)Following parotidectomy performed on one side, mild compensatory hyperfunction was observed on the other side in 8 out 11 cases examined.(5)Hypofunction of the parotid gland was demonstrated in the majority of 10 cases of possible impairment of the parasympathetic secretory nerve in the tympanic cavity following to radical mastoid operation or chronic middle ear infection.(6)The effect of X-ray radiation to the parotid gland was studied in 17 cases.Complete loss of parotid function was observed in those who were thought to had been exposed to more than 5000 r of X-ray.(7)Biopsy of the parotid gland was compared with I131 clearance in 17 cases.It was revealed that the results of I131 clearance test were parallel to the intensity of histologic changes in the acini, and that the changes in the ductal system and striated tubules as well as the presence of lipomatosis had no influence on the results of the clearance test.