Charpy V-notched impact test studies on 21-6-9 austenitic stainless steel at 293 and 77 K demonstrated that hydrogen charging promoted the formation of larger microvoids at 293 K, promoted the formation of facets at 77 K, and reduced the energy absorbed by the material at both temperatures. These observations suggest that the role of hydrogen in the impact behaviour of this material is to enhance whatever crack-growth mechanism is operating at a given temperature. Further, the observation that embrittlement exists even at liquid nitrogen temperatures indicates that little or no localized rearrangement of hydrogen during the test is required or that relatively high strain-rate effects on hydrogen embrittlement need not be necessarily attributed to enhanced transport of hydrogen atmospheres by mobile dislocations. The data presented in this paper are consistent with a model in which the mechanism of hydrogen embrittlement is affected by the extent of plastic deformation.