The effect of temperature on radiation characteristics and subsequent material properties after cryogenic temperature irradiation is analyzed. To date the materials tested have included hot pressed block beryllium, Ti-5% Al-2.5% Sn ELI (Al10AT), and an aluminum alloy 2219. These materials have been irradiated at liquid nitrogen temperatures (140°R) and tensile tested without any intervening warm-up. Some of the liquid nitrogen irradiated and tested material data as well as room temperature data are presented. The properties investigated have included ultimate tensile strength, percent elongation, and fracture toughness. Usually, ductility and the decrease in the magnitude of this property as a function of irradiation is of more vital interest to the designer. The experimental program conducted for some of the NERVA candidate materials is reported and areas of additional investigations for application to advanced NERVA designs are briefly discussed.