In the present work, LBE (lead-bismuth eutectic) embrittlement effects on ferritic/martensitic (FM) steels have been studied by conducting slow-strain-rate tensile (SSRT) testing on T91 and F82H steels either in Ar or in liquid LBE after irradiation to doses up to about 20 dpa in a mixed spectrum of spallation neutrons and high energy protons. SSRT tests were performed at temperatures in the range of 150-500 degrees C. Tests in Ar revealed significant irradiation-induced hardening and embrittlement effects (loss of ductility) as compared to the unirradiated ones. Tests in LBE showed additional embrittlement effects induced by LBE, which increased with irradiation-induced hardening. As a consequence, the fracture strain of irradiated specimens was reduced to a very low level of about 2-3%. A combination of the model of adsorption-induced reduction in cohesion of atomic bonds and the Kelly-Tyson-Cottrell criterion (sigma/tau >= sigma(max)/tau(max)) for brittle cleavage fracture was used to interpret qualitatively the observation reported in the present paper. (C) 2011 Elsevier B.V. All rights reserved.