The FTIR spectra of Wells-Dawson and Keggin type heteropolyacids, H6P2W18O62 and H3PW12O40, respectively, were registered in the course of their dehydration at temperatures between room temperature and 300-350degreesC as well as during the sorption of ethanol on dehydrated and and/or dehydroxylated samples. The changes on heating in the secondary structure of the samples were observed and discussed. Ethanol adsorbed on dehydrated heteropolyacid gets protonated and participates in the formation of secondary structure of heteropolyacid. In the case of dehydroxylated acids physical sorption of ethanol is only observed. (C) 2004 Elsevier B.V. All rights reserved.