Over a period of 18 months the thyroid gland of 31 patients suffering from Grave's disease was examined by Duplex ultrasound for changes in blood perfusion. In 24 of these patients a follow-up study was achieved immediately after a presurgical iodine therapy. For estimation of the perfusion the "Pulsatile Flow Index (PFI)" was calculated. Compared to the normal group (22 volunteers, mean: 0.46 +/- 0.11) changes of 41 and 22% were highly significant for this pre (mean: 0.65 +/- 0.08, p < 10E-6) and post therapy (0.56 +/- 0.1, p < 5E-5). Therapy was unsuccessful in 3 cases on a single, in one case on both sides. Altogether PFI yielded semiquantitative information on blood perfusion of the gland as well as on the rate of success.