The adsorption behavior of benzene on dehydrated NaY zeolite has been studied by means of 129Xe n.m.r. and isotherm measurements of adsorbed xenon followed by proton and 13C n.m.r. of adsorbed benzene. Samples with varied benzene loadings were investigated. We found that to obtain a homogeneous molecular distribution in the zeolite cavities, thermal pretreatment of the sample at temperatures above 250°C for a period of several hours was necessary. The maximum number of benzene molecules that can be loaded within a zeolite supercage is found to lie between 4.9 and 5.2. 129Xe n.m.r. has provided valuable information about the arrangement and mobility of adsorbed benzene. To confirm the effect of heat treatment on benzene distribution within NaY supercages, we also examined the proton and 13C n.m.r. spectra of adsorbed benzene and compared them with published results.