A preliminary study has been completed on how irradiation affects structural materials of high-temperature gas-cooled reactor (HTGR) steam cycle/ cogeneration plant components. A literature search was conducted on irradiation data available for reactor component materials, and results are summarized. Data on materials for the core lateral restraint, core peripheral seal, thermal barriers, and control/power rods are reviewed. Irradiation data on the metals (lowalloy carbon steel, Hastelloy alloy X, alloy 800, and Inconel-718) and on the ceramics (alumina and silica) indicate no major changes on the tensile or creep strengths of the materials occurring at fluences that exceed those found in the HTGR, which are expected to be 1 x 1017 n/cm2 fast and 1 x 1017 n/cm2 thermal. Ductility of most of the metals is significantly reduced and this reduction needs to be considered in design of the components exposed to irradiation. Future work on irradiation effects studies will be focused on the high cycle fatigue behavior of the metals since those data are not yet available. The effects of irradiationinduced creep on the stress relaxation of Inconel-718 core lateral restraint springs also need to be determined.