The author observed TTS and recovery time after exposure of the pure tone stimuli on 10 ears with OMPC patients and compaired it with normal persons. The sound stimulation was performed with 500Hz and 2000Hz at 100dB (I.S.O) for 5 minutes and 20 minutes, respectively. The follwing results were obtained : 1) The amounts of TTS were increased in the normal ears than the ears with conductive hearing disturbance and the increase was more prominent in 2000Hz than in 500Hz and more when exposure to noise for 20 minutes than for 5 minutes. 2) The recovery time was prolonged in normal ears than in ears with conductive hearing disturbance, particularly in 2000Hz and when exposure to noise for 20 minutes. 3) Much individual variation was found in the amounts of TTS and the recovery time of the persons with OMPC, too. 4) The persons with normal ears more often complained of tinnitus during the experiments than the persons with OMPC.