By refering to literatures the author pointed out that some patients who had hearing loss caused by retrocochlear lesions and had no cochlear impairment complain of tinnitus. This is often called central tinnitus. According to the knowledge obtained from the literatures the auditory characteristic features of central tinnitus are speculated as follows. 1) Though some central tinnitus can be easily masked by sound in the contralateral ear, some cannot be masked even by loud sound in the ipsilateral ear. 2) Some central tinnitus cannot be abolished by lignocain which filled up the tympanic cavity and permeated into the cochlea by aids of an iontophoresis technique. 3) Some central tinnitus cannot be suppressed by electrical stimulation of the ear with the round window electrode. However, these speculations have not been confirmed on the cases with hearing loss caused by retrocochlear lesions.
