Pd-Cu composite membranes were made by successive electroless deposition of Pd and then Cu onto various tubular porous ceramic supports. Pure gas (H-2, N-2) permeability tests were conducted at high temperature with simultaneous annealing to induce intermetallic diffusion. Both the alloy composition and the support structure are shown to be responsible for the differences in membrane performance. The highest hydrogen permeability was observed at an alloy composition of 60 wt.% Pd at a constant temperature of 350degreesC. A typical H-2 flux for this membrane was 0.81 mol/m(2).s at 350degreesC and 255 kPa H-2 partial pressure.