Composite Pd/Ag alloy membranes have been prepared and used to study the catalytic dehydrogenation of n-butane in a high-temperature membrane reactor. Conversions obtained by using oxygen and carbon monoxide as sweep gases have been compared to results obtained using nitrogen as a sweep gas and with the equilibrium value for the dehydrogenation reaction. Increases of conversion at 670 K of 4 and 6 fold respectively above the equilibrium value were observed when using CO and O-2 as sweep gases. The potential formation of metallic oxide on the membrane surface was eliminated by a high temperature reduction with H-2 prior to the reaction experiments.