In 37 males and females with thyroid carcinoma, treated with radio-iodine, parotid gland function was investigated before and one week after therapy. 34 subjects remained free of complaints and showed no effect of 'I-therapy on parotid flow rate. Following therapy, all of them showed alterations in the composition of parotid secretion, especially enhanced values for a-amylase activity, protein concentration and sodium concentration. Three subjects developed acute parotitis of the obstructive sialadenitis type. In these patients, flow rate was severely reduced. The values for PHI, sodium, a-amylase and protein in parotid saliva were markedly elevated. Just as in chronic recurrent parotitis, increased activity of salivary glandular kallikrein in radio-iodine sialadenitis was measured.