1. The study of the permeability of composite membrane catalysts towards hydrogen has shown that the application of a layer of palladium alloy with 9.8% ruthenium on a polydimethylsiloxane film increases the rate of hydrogen transport proportionately to the thickness of the alloy layer. 2. At an estimated thickness of the alloy layer of up to 80 nm the layer remains porous and the permeability towards hydrogen is limited by diffusion through the polydi-methylsiloxane film. © 1980 Plenum Publishing Corporation.