The conventional endurance limit does not characterize one specimen but a set of virgin specimens. This present study deals with the determination of the present state of one specimen by its “actual” endurance limit. The connection between the state of a specimen and its thermal response, obtained by using the thermal test method, has already been shown. It is shown here the close correlation which exists between the transition stress value τl and the actual endurance limit of the specimen. Thus, the actual endurance limit of a specimen at any moment in its fatigue life, so, at any stage of treatment, could be determined by using a “nondamaging” method.