The origin of subjective tinnitus is not really known yet. It is possible to investigate the function of outer hair cells by means of the distortion products of otoacoustic emissions (DPOAE).DPOAE of 56 patients were analysed in a prospective study (tinnitus without any loss of hearing n = 34; hearing loss with a maximum of 35 dB and tinnitus n = 22). There was always a normal tympanogram and in no case a conductive hearing loss. The relation of the primary tones f2/f1 was 1.22, the levels of the primary tones were 70 dB.DPOAE-amplitudes were reduced distinctly in both groups of patients. But there was no general difference and no difference at the frequency of tinnitus between the ear with tinnitus and the contralateral ear (no hearing loss) or there was a small reduction related to the normal ear (distinct hearing loss). DPOAE-amplitudes did not change in patients without hearing loss after a treatment with Pentoxifylline i.v., also not at the frequency of tinnitus, although there was a subjective reduction of tinnitus. In patients with hearing loss DPOAE-amplitudes enhanced like the improvement of hearing threshold at the frequency of tinnitus.The low DPOAE-amplitudes are a sign of damaged outer hair cells of the patients. But there is a symmetry of the DPOAE-amplitudes and there is no change of DPOAE after a therapy with Pentoxifylline i.v. in patients without hearing loss.