Békésy audiometry was utilized to show that an abnormal separation of forward and reverse frequency tracing is to be referred to an abnormal fatigability in neurosensorial hearing loss (presbycusis and noise-induced hearing loss). The ascending and descending threshold with continuous tone was compared to fixed frequency per-stimulatory threshold that has been determinated using interrupted and continuous tone. During the study has been evaluated the gap between the continuous and interrupted tone and the excursion amplitude in interrupted and continuous tone. The results are than an abnormal separation between forward and reverse frequency tracings is connected to an abnormal fatigability. Thus, according to other authors, forward-backward Békésy audiometry can be used to show a retrocochlear pathology in the considered hearing loss.