We have attempted a quantitative evaluation of the iodine taken in with the thermal waters from Salsomaggiore during therapeutic bathing, inhalation (dry and damp spray), or ingestion. For this purpose to 127I we have applied the metabolic parameters obtained through a 131I inhalation test and a 125I ingestion test. Of the iodine inhaled by aerosol 45% becomes exhaled; by 24 hours 2% is in the serum and in the extra-thyroid area of iodine distribution, 16% in the thyroid, 16% in the urine. By adding the amount of iodine exhaled to that found in the metabolic cycle of iodine, we find that about 21% of the inhaled iodine is still missing. This amount is trapped in the respiratory tract from where it disappears only very gradually. At the end of the 24 hours, therefore, in the metabolic cycle of the iodine we find 34% of that inhaled, whereas we find 87% of that ingested. The level of iodine in the serum reached in thermal therapeutic inhalation, never stays at a level which might alter the functioning of a normal thyroid. The amount of inhaled iodine which is excreted with the urine is usually eliminated during the first excretions. Experimental studies suggest that the iodine taken in during bathing in the thermal-pools mainly comes from iodine released from the water through the addition of hypochlorites, and is then inhaled through breathing the air just above the water.