Hydrogen adsorption on Rh/Al2O3 catalysts sintered at increasing temperatures has been analyzed with high-resolution electron microscopy (HREM), proton nuclear magnetic resonance (H-1 NMR), and microcalorimetric techniques. The H-1 NMR technique has been used to differentiate hydrogen adsorption on metal particles from that produced on the support. Metal dispersions estimated by HREM are intermediate between those deduced from volumetry and NMR techniques. Metal particle sizes deduced from HREM histograms, once weighted for surface effects, agree well with those determined by NMR but differ appreciably from those calculated from volumetric data. Observed differences have been ascribed to hydrogen retained on Al2O3 near Rh particles, that increases the NMR line located at the resonance frequency. The dependence of the NMR shift associated with hydrogen adsorbed on the rhodium is discussed in terms of metal particle size. In samples with low metal loadings, a partial coverage of metal particles with Al2O3 moieties, deposited during catalyst preparation, has been detected that reduces observed H-1 NMR shifts.