Results are presented from low temperature hydrogen permeation experiments using a palladium/copper membrane. Inlet pressure was varied from 5 psig to 180 psig, while temperature was varied from 25 degreesC to 275 degreesC. The palladium/copper membranes exhibited flow stability problems at low temperatures and pressures when using ultra high purity hydrogen. A preconditioning step of high temperatures and inlet pressures of pure hydrogen was necessary to stimulate any substantial permeate flows. After pre-conditioning, results showed zero hydrogen flow when using 3 - 4% hydrogen mixed with helium or argon. It is thought that the inert gas atoms were adsorbed into the membrane surface and thus blocked the hydrogen atom dissolution. When using pure hydrogen at low to moderate temperatures and low pressures, no measurable permeate flow was observed. Also, zero permeate flow was observed at relatively high temperatures (e.g., 150degreesC) and a low inlet pressure (5 psig). The cause of the zero permeate flow, when using pure hydrogen, was attributed to interface control of the permeation process. Interface control could be due to: ( a) insufficient energy to split the hydrogen molecule into hydrogen atoms, or (b) a reversible phase change from beta to alpha of crystals at the near surface. (C) 2003 Kluwer Academic Publishers.