The concentration of Zablocka Thermal Brine that contains iodine was studied in order to prepare a concentrated solution of the curative salts. The membrane distillation process was used for the concentration of brines with two kinds of polypropylene Accurel PP membranes. The solutions were concentrated from 34 to 310 g NaCl/L, and the iodine concentration increase up to 1 g l(-/)L was achieved. The mineral composition of concentrated solutions, including the iodine content was determined using an ion chromatography method. The obtained rejection of solutes was close to 100%, but the small amounts of NH3 and 12 also diffused together with water vapor through the membrane. However, the concentration of brines using the membrane distillation process allows achieving significantly lower losses of iodine in comparison to the traditional evaporation methods. An increase in the solute concentration (to 310 g NaCl/L) caused a 30-50% drop in the yield of water evaporation through the membrane. Moreover, an intensive membrane scaling was observed, especially during the initial period of feed concentration. (C) 2013 Elsevier B.V. All rights reserved.