Several stainless steels and Ni-base alloys were investigated to compare their hydrogen embrittlement susceptibility in annealed, cold-worked, and aged conditions. Cathodic hydrogen charging was used for introducing hydrogen, and reverse bending tests were applied in measuring hydrogen-induced ductility loss. It was found that hydrogen embrittlement increased with increasing nickel content, cold-working and thermal aging at 500degreesC. Optical metallographic examination and X-ray diffraction analysis showed substantial microstructural and structural changes in all the materials under investigation, but the standard and highly alloyed stainless steels in cold-worked and cold-worked and aged cases were more resistant to hydrogen-induced ductility loss than highly corrosion resistant Ni-base alloys. (C) 2002 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy.