An experimental investigation was carried out to examine the role of inclusions and particles in the microfracture process in a hardened and tempered NiCrMo steel. The study was confined to two kinds of loading situations, namely uniaxial tension and the plane strain condition. The experimental programme included quantitative analysis of inclusions, evaluation of tensile and fracture toughness values, quantitative microfractography for dimple size analysis and area fraction determination. The most probable inclusion size and the interinclusion spacing are found to lie in the ranges 0.8–1.6 μm and 2–4 μm respectivly. The ratio of the size of the dimple to the size of the inclusion initiating the dimple lies between 2.0 and 5.5 under the plane strain condition. Microfractography revealed that the tendency to fracture by the microvoid coalescence mode increases with the applied stress intensity level. The dimple size appears to depend on the triaxiality factor in the specimen and was found to be two to five times larger in plane strain fracture toughness specimens than in tensile specimens.