A test device has been developed at P' Institute in order to investigate the mechanical behaviour of structural materials under high pressure of gaseous hydrogen. In this paper, preliminary results on fatigue crack propagation in a martensitic stainless steel are presented. A tremendous fatigue crack growth enhancement is observed at high pressure (9 MPa). This enhancement is dependent of pressure. It is noticed that the maximum enhancement is associated with a brittle fracture mode. However no intergranular decohesion is noticed in this regime. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.