Earlier studies have classified deafness cases into two general groups, those having functional disorders of the middle ear and those having impairments resulting from atrophy of the nerve fibers terminating along the basilar membrane (conductive and nerve deafness types, respectively). Such classifications have been made using bone conduction threshold measurements and unilateral loudness balance results as the basis for differentiation. Bone conduction results, however, are often subject to considerable error while the unilateral loudness balance technique can only be applied to individuals having one normal and one impaired ear. These limitations introduce a need for a completely independent monaural method of classifying deafness types. This is particularly true for the selection of candidates suitable for the fenestration operation for the restoration of hearing in otosclerosis (immobilized stapes). The present paper is concerned with an investigation of short time auditory fatigue as a method of obtaining an impairment analysis. In this study, it was found that the fatigue of the conductively deafened observer was similar to the normal observer except the onset of fatigue was shifted by the amount of the threshold loss. For the nerve deafened observer, on the other hand, the onset of fatigue was found to occur at normal intensity levels. The occurrence of excessive fatigue in one of the nerve type impairment cases investigated appears to offer additional information on the nature of the lesion.