Pd based membranes have the potential to separate hydrogen from gas streams due to the unique permeation properties of Pd metal to hydrogen. However, thin films of the metal are required in order,to obtain the necessary flux; this is usually achieved by deposition onto a porous substrate. Because of its simplicity and low cost, electroless plating has been used in the present work to deposit Pd as a thin film onto a porous alumina substrate. Due to non-uniform activation of the substrate surface and/or impurities present in the plating solution, defects occur in the Pd film. These defects can be repaired by the technique of electroless plating combined with osmosis. By this method a membrane with an initial H-2/N-2 permeation ratio of 10 could be repaired to give an increase of this ratio to approximately 1000. The hydrogen permeation performance-of the resultant membrane was investigated using pure hydrogen at temperatures from 320 to 577 degrees C. (C) 2000 Elsevier Science B.V. All rights reserved.