Following high dose radio-iodine therapy, some radiation damage to the salivary glands is to be expected since iodine is taken up by these glands. The great individual variation in the uptake makes it impossible to predict the severity of the damage. T max and maximal excretion capacity after stimulation were therefore estimated by a camera functional scintigram with digital read out in patients following radioiodine therapy (0.1-3.2 Ci); the excretion index was used as an indirect measure of salivary flow. After a dose up to 0.3 Ci there is a change of T max and maximal excretion capacity in 30% of patients; after a dose of 0.5 to 1 Ci it is found in 60 and 80% and after very high doses of 1.1 to 3.2 Ci an abnormal Tmax was found in two-thirds of all patients and reduced or absent excretion capacity in all nine patients in this group. The excretion index also depended significantly on the cumulative dose. All patients who had received very high doses showed marked hyposialia or asialia. The early results of interim examinations suggest, similar to radio-iodine induced hypothyroidism, a cumulative risk of reduced function. In view of the long survival period of patients with differentiated thyroid carcinomas attention should be drawn to this side effect.