FTIR and NMR spectroscopy have been applied to quantification of Bronsted acid sites in various mordenite samples. A standardised deconvolution procedure has been developed for reliable decomposition of the complex hydroxyl region in the infrared spectra of mordenites into high frequency and low frequency peaks, and the peak extinction coefficients have been determined. As a result, the overall number of Bronsted acid sites, their distribution between main channels and side pockets, and the amount of extraframework aluminium can be determined, Results obtained by both FTIR and NMR are in good agreement and support each other. For instance, it is shown that for fully exchanged H-MOR, the distribution of Bronsted hydroxyls between main channels and side pockets is approximately 2:1. On partial ion exchange Na-MOR --> HNa-MOR, protons are first introduced into main channel sites, with Na remaining in the side pockets.