The NMR spectroscopy of xenon sorbed in beds of ZSM-5 zeolite is used to study the rate of adsorption of benzene molecules from the gas phase, as well as the rate of the combined process of adsorption and desorption in a bed consisting of two types of crystallites, some being initially benzene-loaded, some not. The exchange rate is shown to depend dramatically on the crystallite arrangement. The magnitudes of the observed rate constants and line shifts are confirmed by calculations based on simple models.