Many different classes of materials are required in the development of advanced Rankine systems. These materials include nuclear fuels in the reactor, refractory metal alloys for alkali metal containment, electrical materials for the alternator, and stainless steel for the radiator. The ceramics uranium carbide and uranium dioxide are presently being considered as reactor fuels for this system. Of the numerous refractory metal alloys available, the tubing alloys FS-85 (Cb-10W-28Ta-1Zr), T-111 (Ta-8W-2Hf), and T-222 (Ta-10.4W-2.4Hf-0.01C), have survived the welding, thermal aging, and mechanical property screening tests. Based on long-time creep data, the alloys TZC (Mo-1.25Ti-0.15Zr-0.12C), TZM (Mo-0.5Ti-0.08Zr), and Cb-132M (Cb-20Ta-15W-5Mo-2Zr-0.13C) appear the best for turbine rotor applications. Long-time property data are becoming available for electrical materials for applications up to 1000°F, and new electrical materials are being developed for higher temperatures. Cermets with properties suitable for applications as alkali-metal-lubricated bearing materials are available. Stainless steel operating below 1400°F will probably be used in radiators for this system.