Because of the high thermal and mechanical stresses in components of a helium turbine coupled directly to a high-temperature reactor and the stringent nuclear safety requirements, an extensive materials development program has been undertaken. The candidate alloys for turbine blades and hot ducts (nickel- and molybdenum-base alloys) and for rotors (1% CrMoV and 12% chromium steels) have been tested under the expected service conditions. The results of creep/rupture, fatigue, and fracture mechanics tests on turbine blade and rotor materials are presented. The gas/metal reactions that occur in the simulated reactor coolant gas and the decontamination behavior of components are also discussed. In addition the development of a molybdenum-base alloy for turbine blading is reported.