The distribution of surface aluminum atoms among different coordination states is a key to the understanding of the acidity of aluminas and zeolites. Single-pulse Al-27 MAS NMR spectra do not distinguish the surface from the bulk species. Proton-aluminum cross-polarization (CP-MAS) spectra, when hydroxyls are the source of protons, give a biased representation of the surface topology. Indeed, water chemisorption involves an unknown number of reconstructed layers because chemisorption is dissociative. On the other hand, when CP is operated from chemisorbed ammonia, the distribution of the surface Al is observed, and it represents the state of the active catalytic surface. It was the main purpose of this work to study the nature of Lewis acidity in various catalysts (aluminas and zeolites) pretreated under controlled atmosphere at different temperatures. Isotopically enriched ammonia (NH3)-N-15 chemisorption was employed to probe the surface active sites and to allow for magnetization transfer to surface and close-to-surface Al nuclei. A special deconvolution procedure was applied to obtain Al-27 spectral parameters for different Al sites in partially resolved spectra. The procedure accounted for the normal distribution of electric field gradient tenser components at a particular site. It is shown that there are two kinds of Lewis sites on aluminas : namely, a tetrahedral site with isotropic shift of about 58 ppm and quadrupolar coupling constant QCC similar or equal to 6 MHz and a pentagonal site with a isotropic shift of about 40 ppm and a slightly smaller QCC. In zeolites the same kinds of sites exist in the nonframework aluminum debris, and in addition, the Bronsted sites are associated with framework aluminum.