Charpy V-notch and drop-weight specimens were used to determine changes in transition temperature for various steels and weld metals irradiated in different nuclear and thermal environments to integrated fast neutron flux exposures to 2 × 10¹⁹ nvt (<1.0 Mev). The Brookhaven Graphite Reactor, the Oak Ridge Low-Intensity Test Reactor (LITR), and National Reactor Test Station Materials Testing Reactor (MTR) were used for the irradiations at temperatures under 200 F and at 575 F. Irradiations to integrated fast neutron flux levels of 5 × 10¹⁸ nvt effected 40 to 100 F shifts in transition temperature. Increasing the irradiation temperature from 200 to 575 F significantly decreased the radiation-induced damage. Transition temperature shifts in the order of 250 F were developed in materials irradiated at temperatures less than 200 F to an integrated fast neutron flux dosage of 1 × 10¹⁹ nvt. Postirradiation heat treatment revealed that a recovery of properties may be obtained by annealing. Comparison of Charpy V and drop-weight nil-ductility transition temperature shifts for 20 irradiation experiments demonstrated excellent correspondence in the evaluation of irradiation effects by these two test methods.