The surface preparation dependent interactions of pyridine with ..gamma..-alumina are explored with solid-state /sup 15/N and /sup 2/H NMR spectroscopies. The observation of pyridine-/sup 15/N adsorbed to the surface reveals two resonances which are both characteristic of pyridine participating in a Lewis acid-base complex. These resonances display only partial tensorial averaging, and full information about the motionally averaged tensors is derived from magic angle spinning sideband simulations. Both resonances are assigned to complexes containing coordinatively unsaturated surface aluminum cations which occupy tetrahedral and octahedral sites in the defect spinel lattice. The relative distributions of tetrahedral and octahedral Lewis acid sites are determined as a function of surface preparation conditions, and the results are used with a simple surface preparation model to calculate the relative contribution of the various low index lattice planes to the composition of the surface. /sup 2/H NMR line-shape studies of pyridine-..cap alpha..,..cap alpha..'-d/sub 2/ on ..gamma..-alumina indicate a heterogeneous distribution of pyridine motional species, which reflect the physical and steric characteristics of the surface binding sites. Quadrupolar spin-echo line-shape simulations for various motional models indicate the significant contributions of pyridines undergoing continuous diffusion or twofold ring flips about their twofold symmetry axis.