The hydrogen permeation behaviour of iron-and nickel-based amorphous alloys was characterized using electrochemical methodology and compared with the properties of crystalline metals and alloys. The materials studied were amorphous Fe40Ni38Mo4B18, Fe74Ni4Mo3B17, Fe78B13Si9 and Ni81P19, as well as a crystalline low-carbon steel, pure nickel and pure palladium. The double potentiostatic electrochemical hydrogen permeation tests were performed at 40 degrees C using a 0.1 N NaOH solution as electrolyte. It was found that the hydrogen diffusivity in the iron-based amorphous alloys is a few orders of magnitude lower than in carbon steel and iron, while a much smaller difference exists between Ni81P19 and pure nickel. Furthermore, the amorphous alloys showed a strikingly greater capacity to dissolve hydrogen in solid solution compared with their crystalline counterparts. In some cases, their apparent hydrogen solubility was even greater than that for the liquid metal of the main element present in their chemical composition.