Experiments comparing the embrittling effects of high-energy (10-MeV) electrons and test reactor fast neutrons have been performed to elucidate the role of primary damage state on reactor pressure vessel embrittlement. Electrons produce displacement damage primarily by low-energy atomic recoils, while fast neutrons produce displacements from considerably higher energy recoils. Comparison of changes resulting from neutron irradiation, in which nascent point-defect clusters can form in dense cascades, with electron irradiation, where cascade formation is minimized, can provide insight into the role that the in-cascade point-defect clusters have on embrittlement mechanisms. Yield strength changes induced by 10-MeV electrons or test reactor neutron irradiations of unalloyed iron and an Fe-0.9 wt.% Cu-1.0 wt.% Mn alloy were examined up to 1.5 x 10-2 dpa. The small alloying additions substantially enhanced embrittlement in both the electron- and neutron-irradiated samples relative to unalloyed iron. Similar embrittlement trends with increasing radiation damage were observed for electrons and neutrons in both the ternary and unalloyed iron. Preliminary results of small-angle X-ray scattering measurements of embrittled microstructures are also reported.