The influence of epsilon-martensite on the cryogenic toughness of an Fe-1 7 wt % Mn alloy was studied in this work. Alloys were tempered at various temperatures in order to systematically increase the volume fraction of epsilon-martensite. This was followed by Charpy impact testing conducted at room temperature and at - 196-degrees-C. The experimental results indicated that although room-temperature toughness was not influenced by the epsilon-martensite content, the cryogenic toughness was strongly dependent on the volume fraction of epsilon-martensite. In particular, with the exception of the alloys tempered at 400 and 450-degrees-C, the impact toughness consistently increased with epsilon-martensite content. Microstructural and fractographic evaluations using SEM and TEM suggested that the toughness improvements were attributed to the epsilon --> alpha stress-induced martensite transformation. No microstructural evidence was found which could be ascribed to an effect of epsilon-martensite on the low-temperature embrittlement exhibited by Fe-Mn alloys tempered at 400-450-degrees-C.