Fourier transform infrared spectrometry was used to study adsorption of dihydrogen on M⁺-ZSM-5 zeolites (M = Li, Na, K). Interaction of the adsorbed molecule with the zeolite adsorption centres renders the fundamental H-H stretching mode infrared active; the corresponding absorption bands appeared at 4092, 4101 and 4112 cm^-1 for the Li, Na and K exchanged zeolite, respectively. From series of variable-temperature infrared spectra, for which integral absorbance, temperature and hydrogen equilibrium pressure were simultaneously measured, thermodynamic characterization of the adsorption process was accomplished. The standard adsorption enthalpy resulted to be -6.5, -10.3 and -9.1 kJ mol^-1 for H₂/Li-ZSM-5, H ₂/Na-ZSM-5 and H₂/K-ZSM-5, respectively. For the standard adsorption entropy corresponding values were found to be -90, -121 and -124 J mol^-1 K^-1, respectively.