In order to develop speech enhancement methods for the hearing impaired, acoustical and auditory factors affecting on the voicing distinction for stop consonants in V1CV2 contexts were examined. The effects of the level of V1 and the silent interval between Vt and C on the voicing distinction for stops in V1CV2 contexts were examined in Experiment I. And, the effect of the fundamental frequency on the voicing distinction for stops in V1CV2 contexts was examined in Experiment II. The following results were obtained. 1) The identification rate for the voiced stop Ibl decreased when the level of V1 decreased when the VOT was fixed at 30ms. 2) The identification rate for the voiced stop /b/ decreased when the silent interval between V1 and C increased when the VOT was fixed at 30ms. 3) Sensori-neural hearing- impaired subjects needed a longer silent interval compared to normal subjects to identify /p/. 4) Normal subjects needed a longer silent interval to identify /p/ when the presentation level was lower. 5) When the lower the F0 was, the longer the dt needed to detect unvoiced stops.