One technique of using nuclear energy for propulsion of a rocket system involves the use of a fission reactor as a heat source for a combination coolant-propellant. One of the factors that will influence the performance of this type of vehicle will be the radiation resistance of the materials, parts, and components that are used in its design. Another important factor is the effect of nuclear radiation on materials at cryogenic temperatures. This paper presents a discussion on the effects of nuclear radiation on materials exposed to a cryogenic environment. Sealing materials, lubricants, thermal insulation, and structural materials are discussed with respect to radiation stability. Some experimental data on the effects of simultaneous exposure of metals to nuclear radiation and cryogenic temperatures are also presented.