The effects of radiation therapy on salivary function of parotid gland were studied 20 male patients by radiation for tumors of head and neck. Saliva samples were collected before, during the radiotherapy and follow up. Parotid salivary function was quantitatively evaluated using a sialometry, sialochemistry, and scintigraphy. Salivary flow rates decreased in all individuals after irradiation. Glands than were partially irradiated were more likely to have some residual function than fully irradiated glands. Sodium and chloride contents were increased in parotid saliva of radiation patients where as potassium content was not changed definitively, pH was not changed during radiotherapy, but increased during follow up period. Scintigraphic stimulatory response rates showed similar result as flow rates. These results showed that exclusion of partial parotid gland from radiation is necessary to prevent severe xerostomia.