A procedure was developed for studying the thermodynamics involved in the interaction of carbon monoxide with Brønsted acid sites in zeolites, without the need for microcalorimetric measurements. The observables are the integrated infrared intensity of the C-O stretching mode of the OH···CO adducts, temperature, and equilibrium pressure. These quantities were measured by means of variable-temperature IR spectroscopy, using a home made IR cell equipped with a capacitance pressure gauge. Interaction of CO with Brønsted acid sites at the supercage of the faujasite-type H-Y zeolite involves a standard enthalpy change, ΔH° of -25.6 kJ mol^-1, and a standard entropy change, ΔS° of -161 J mol^-1 K^-1. These values were compared with the corresponding figures obtained from the calorimetric determination of CO adsorption on a number of metal oxides and zeolites.