Due to high volatility and environmental mobility, radioactive isotopes of 
iodine pose a serious risk in the acute phases of a nuclear accident. The 
critical organ for iodine is the thyroid. A number of studies dealing with 
thyroid protection from exposure to radioiodine have shown that radioiodine 
uptake by the thyroid can be effectively blocked by administration of stable 
iodine, usually in the form of potassium iodide (KI) pills. However, unless 
perfectly timed, this protective action may be counterproductive. The 
International Atomic Energy Agency recommends potassium iodide prophylaxis in 
cases when an avertable thyroid dose by protective action exceeds 100 mGy. This 
paper reviews experiences and practices with potassium iodide in the thyroid 
protection. This kind of information should serve as the basis for discussion 
and decision making on KI prophylactic programmes in nuclear emergency 
situations in Croatia. If Croatia adopts such programme, it will still have to 
develop the most effective way of KI stockpiling and distribution or 
predistribution.