Yield stress and hardness changes have been demonstrated to be strongly correlated to transition temperature shifts in nuclear pressure vessel steels, and hence such measurements can be a convenient means for evaluating the role of metallurgical and environmental variables in embrittlement. We have irradiated miniature tensile specimens of over 100 alloy (chemistry and thermomechanical treatment) variants at nominal fluxes 0.5 to 5 × 10¹⁶ n/m²·s, temperatures 271 to 325°C, and fluences 0.15 to 3 × 10²³ n/m². A subset of these specimens has been tested, and the results are reported here. For both commercial and model alloys, good agreement between hardness and yield stress changes were observed. Yield stress changes were strongly influenced by copper and nickel content and by thermomechanical treatment.