The structural changes in Pd and Pd–Ru alloys induced by the repeated absorption–desorption of hydrogen have been studied. It is found that absorption–desorption cycles produce structural changes in Pd whereas the addition of small amounts of Ru inhibits these hydrogen‐induced changes. The experimental results show that bulk hydrogen absorption occurs in Pd, while hydrogen surface adsorption becomes dominant over bulk absorption, in the Pd–Ru alloy. ©1995 American Institute of Physics.