Multinuclear solid-state NMR and infrared spectroscopy have been applied to investigate the host-guest interactions and the nature of the adsorption sites of pyrrole on alkali-exchanged zeolites Y (LiNaY, NaY, KNaY, and CsNaY). The presence of pyrrole provokes changes in the MAS NMR spectra of Na-23, Li-7, and Cs-133 to a degree dependent upon the amount adsorbed. The decrease in the quadrupolar coupling constant for 23Na as well as the shift for Li-7 and Cs-133 signals are attributed to the interaction of the canon with the pyrrole ring system. The adsorption of pyrrole induces the displacement of rations located at SI' and SII sites toward the supercage to bind the guest molecules. In this way, the distribution of the rations at nonframework sites depends on the amount of adsorbate in the zeolite. At low loadings, pyrrole molecules bind preferentially to more eleotropositive ration in partially exchanged zeolites Y. Quantitative analysis by H-1 NMR shows that the canon-pyrrole complexes formed possess a stoichiometry of 1:1. The origin of the basic site heterogeneity, evidenced by the presence of several components in the -NH infrared stretching band, is investigated assuming that the heterocycle of pyrrole interacts with rations at SII sites in the supercage and the -NH group forms a hydrogen bond with a basic oxygen atom placed in the framework six-member ring. Making use of the information derived from NMR, it is concluded that the main source of basic site heterogeneity comes from the number of aluminum atoms in the six-member rings of the Sil site where the alkaline ration is located.