Permeation across metallic membranes is a process used in the industry for purifying hydrogen. In conventional technology, a few tens of micrometers thick metallic membranes made of palladium alloys are used in the 400-600 degrees C temperature range, using a driving force of several bars for enhanced kinetics. In stationary conditions of flow, the diffusion-controlled transport of atomic hydrogen across the membrane is usually rate-determining. When thin (sub-micron thick) membranes are used, surface rate contributions become more significant. To optimize permeation performances, there is therefore a need for separately measuring surface and bulk rate contributions. In this communication, we report on the kinetics of hydrogen permeation across Pd77Ag23 metallic membranes using pneumato-chemical impedance spectroscopy. The role of different operating parameters (temperature, surface state, membrane microstructure) on the kinetics of permeation is analyzed and discussed. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.