It is common knowledge that hydrogen influences the slip of dislocations in f.c.c. metallic materials in the sense of a localized slip planarity. However, the extent to which planar slip and the altered stacking fault energy due to this so-called HELP-mechanism affect the strain rate sensitivity is still unknown. Single- and nanocrystalline nickel specimens were investigated by strain rate jump tests in the nanoindenter and an increase in the strain rate sensitivity was found by in situ electrochemical charging with hydrogen from the backside of the specimens. Together with a decrease in hardness, the effect can be attributed to a decreased activation volume for dislocation motion in the presence of hydrogen.