The effect of neutron radiation on the impact and tensile properties of ASTM A 302 grade B, SA-336, and HY-65 high-strength pressure vessel steels, and weld metal deposited with types E9016 and E10016 electrodes were studied. Standard size Charpy V-notch and subsize tensile specimens of these materials were irradiated at a reference temperature of 500 F in a dry air atmosphere to an integrated flux of between 2 × 10¹⁸ nvt and 3 × 10¹⁸ nvt (>0.4 ev) at Brookhaven National Laboratory. HY-65 steel specimens were also irradiated to the same integrated dose at 650 F. Several heat, treatment conditions were represented in the A 302 grade B and HY-65 materials. Control specimens were heated for an equal time at the temperatures of the irradiated materials. Brittle to ductile impact transition curves and tensile values were determined lor both the controls and irradiated specimens. The materials irradiated at 500 F were appreciably embrittled. Embrittlement did not occur in HY-65 specimens irradiated at 650 F. Tensile strength and tensile ductility were not, or only slightly, affected in all cases.