The ear is fatigued by a note of known frequency and known absolute intensity. The decrease in aural sensitiveness caused by exposure to this note is found by making a series of threshold measurements at short consecutive intervals after the cessation of the sound. The note used for threshold measurements is 410 c./sec., while for the fatiguing note both this frequency and others, within a range of 25 c./sec. to either side, are used, at two widely separated levels of intensity. When threshold determinations are made at the frequency of the fatiguing note, the duration of the auditory fatigue increases with the intensity of the fatiguing stimulus to attain rapidly a maximum value. At any frequency below or above that of the fatiguing note, the duration of the fatigue again increases with increase in the intensity of the fatiguing tone, but does so less quickly. The range of frequency over which auditory fatigue is apparent decreases as the intensity of the stimulus decreases. The results are shown to be consistent with the resonance theory of hearing.