Defect-free Pd membranes were prepared by an electroless plating technique on porous stainless-steel tubes. The effective surface of Pd membranes was up to 75 cm(2). The helium flux was not detected at room temperature and pressure difference of 3 atm. At 350 degrees C hydrogen permeances of up to 8 m(3)/(m(2).(h) over right arrow.atm(0.5)) were obtained, At a pressure difference of I atm and 350 degrees C, selectivity coefficients as high as J(H-2/J(N-2) = 5,000 were observed. Fluxes of gases, impermeable through the Pd, were quantitatively described as a combination of Knudsen diffusion and viscous flow through the gaps created in rite Pd layer tit high temperatures. The stability of the prepared membranes at temperatures up to 700 degrees C was investigated. The membranes were stable at 350 degrees C over a period of I, 100 h, with no significant changes in the steady-state hydrogen flux and with a recrystallization texture and aggregation of Pd grains.