A number of properties in steel components are detrimentally influenced when exposed to hydrogen environments. Under these conditions, atomic hydrogen is adsorbed on the steel surface, then absorbed and preferentially transported towards tri-dimensional stressed regions in the crystal lattice and into defects such as interfaces or dislocations. The hydrogen embrittlement susceptibility is strongly influenced by various microstructural parameters including the type of inclusions, steel composition and heat treating conditions. One of the alternatives employed in minimizing hydrogen embrittlement is the use of surface barriers for hydrogen permeation. In particular, the presence of surface nitride layers in steels can be considered as an effective barrier. Nitride steel surface layers can be produced by plasma nitriding with the concomitant benefits of improved surface hardness, as well as superior wear and fatigue resistance. Accordingly, in this work, the role of surface nitriding on the exhibited hydrogen permeability was investigated. For this purpose, an API X52 steel was subjected to plasma nitriding to promote the development of surface nitride layers. The surface layer produced was found to consist of a continuous gamma'-Fe4N compound, with a layer of residual austenite and a diffusion zone beneath gamma'. Electrochemical measurements performed in these steels indicated that the hydrogen permeability was significantly reduced in the steel that contained the surface nitride layers. Apparently, the presence of multiple interfaces developed by plasma nitriding and the development of a continuous iron nitride layer play a strong role as effective hydrogen barriers. In particular, a determination of the effective diffusion coefficients D-eff (m(2)s(-1)) in nitrided and non-nitrided API X52 steels indicated that the presence of nitride layers on the steel surface lead to a reduction in hydrogen diffusivity D-eff = 9.41x10(-12) (m(2)s(-1)) when compared with the one corresponding to the non-nitrided steel D,, = 4.32x10(-11) (m(2)s(-1)).