This paper shows the applicability of infrared spectroscopy (IRS) to investigate chemical deterioration of ion exchange resins. The ion exchange systems considered are used in the food industry. The following processes are discussed. Exposing of strong anion exchange resins to the combined influence of a strong alkali and elevated temperature results in chemical altering and/or loss of the functional groups. Organic dyes present in solutions generated in the food industry are accumulated in the resin phase. The dyes are physically fixed in the cation exchange resin. No covalent bonds are formed. Some organic substances can be altered in the resin phase and the products can be irreversibly sorbed by the resin. The combined influence of different deteriorating factors is considered as well. Conclusions based on the IRS investigations are confirmed by chemical experiments. A possible complete interpretation of the IR spectra was carried out for the systems considered. (C) 2002 Elsevier Science B.V. All rights reserved.