Owing to the presence of the fibres which provide a homogeneous reinforcement, it has been possible to combine, in the whole nickel-base matrix of a unidirectionally solidified composite, fatigue life and fatigue strength conditions which cannot be attained in an ordinary material except in high-stress concentration regions where the observation is usually impossible. Taking advantage of this ideal material, two complementary observation techniques, the high-voltage electron microscope (1 MV) and the field-emission gun scanning electron microscope, have not only revealed deformation microstructures such as dislocation multipoles which may be responsible for vacancy production, but also some unusual aspects of the fatigue fracture surfaces which may be most probably attributed to the presence of a supersaturation of vacancies and to their further condensation. These last results, which were obtained at room temperature, may be correlated with the observations performed on ordinary materials but at...