131I-19-iodocholesterol has been used by Beierwaltes et al., to visualize human adrenal glands. The tissue distribution of 131I-19-iodocholesterol was determined by Morita et al., both in dogs and men. No data have been reported on thyroidal 131I accumulation after administration of the radiopharmaceutical. We calculated the percentage uptake of radioactivity in the human thyroid gland inhibited with various therapeutic agents (triiodothyronine (T3), Lugol's solution, potassium perchlorate (KC104).