Hydrogen permeation through unnitrided and nitrided iron membranes was studied by the electrochemical technique. The membranes were charged with hydrogen by cathodic polarization in O.1M,NaOH. It was found that nitriding significantly reduced the permeation rate of hydrogen. Diffusivities and concentrations of hydrogen were calculated for an outer compound (nitride) layer, an inner diffusion layer, and an unmodified iron substrate. The reduced absorption of hydrogen by the nitrided membranes was explained in terms of the hindrance of the entry of hydrogen into the compound layer (the surface effect) and the hindrance of its transport in the compound and diffusion layers (the barrier effect).