Since differentiated thyroid cancer has an excellent prognosis, reduction of long-term side effects of high-dose radioiodine treatment (HD-RIT), i.e. salivary gland impairment is important. Thus, radioprotective effects of amifostine were studied. Salivary gland function was quantified by scintigraphy both in rabbits and patients. Fifteen rabbits were studied prior to and up to 6 months after HD-RIT applying 2 GBq 131I. Ten animals received 200 mg/kg amifostine prior to HD-RIT, and five served as controls. Animals were examined histopathologically. Fifty patients with differentiated thyroid cancer were evaluated prospectively prior to and 3 months after HD-RIT with either 3 or 6 GBq 131I in a double-blind, placebo-controlled study. Twenty-five patients were treated with 500 mg/m2 amifostine intravenously prior to HD-RIT, and 25 patients receiving physiological saline solution served as controls. Complete ablation of the thyroid was achieved in all rabbits four weeks after HD-RIT. In control rabbits 6 months after HD-RIT parenchymal function was reduced significantly (p < 0.0001) by 75.3 +/- 5.3% and 53.6 +/- 17.4% in parotid and submandibular glands, respectively. In contrast, in amifostine-treated rabbits parenchymal function was not significantly reduced. Histopathologically, marked lipomatosis was observed in control animals but was negligible in amifostine-treated animals. In control patients, salivary gland function was significantly (p < 0.001) reduced by 40.2 +/- 14.1% and 39.9 +/- 15.3% in parotid and submandibular glands, respectively, three months after HD-RIT, and 11 patients developed xerostomia. In 25 amifostine-treated patients, salivary gland function was not significantly reduced (p = 0.691), and xerostomia did not occur. Thus, parenchymal damage in salivary glands induced by high-dose radioiodine therapy can be reduced significantly by amifostine. This may improve quality of life of patients with differentiated thyroid cancer.