As is proved by nuclear disaster in Chernobyl Nuclear Power Plant (NPP), iodine prophylaxis may be respected as one of the most urgent and effective methods of prevention of radiation injury of the thyroid gland in the population affected. Author has studied factors and methods of its efficacy and reliability. On the basis of experiments in rats, analytical ways of determination of the dietary iodine intake (iodine supply) of people living around NPP Paks (Hungary) as well as compartment modelling, experiments it is shown, that for optimisation of iodine prophylaxis in masses it is very important to increase the iodine supply up to the recommended values. Combined use of decreased doses of potassium iodide and perchlorate was found to be the optimal way for removal of radioiodine from pregnant organisms and their offsprings following accidental intake of radioiodine.