Thin (0.1-1.5 mu m) Pd and Pd/Ag alloy membranes have been prepared on porous ceramic substrates consisting of a macroporous alpha-Al2O3 disk coated with a sol-gel derived, mesoporous gamma-Al2O3 top layer. Metallorganic chemical vapor deposition (MOCVD) and magnetron sputtering were used to coat the thin metallic membranes employing Pd(II) acetylacetonate and a 75% Pd-25% Ag alloy target, respectively. The gas transport properties of the thin metallic membranes were determined by multicomponent permeation experiments with He, H-2 and Ar at 25-300 degrees C and 1 atm total pressure. The H-2 permeance and H-2 : He selectivity were in the range 1.0-2.0 x 10(-7) mol m(-2) s(-1) Pa-1 and 30-200 at 300 degrees C, respectively. The dependence of H-2 permeation rates on membrane thickness and temperature suggest that surface reaction steps are rate-limiting for H-2 transport through the thin, ceramic-supported metallic membranes made by MOCVD and sputtering.