The following experiment of vibration exposure was performed with a similar method on the basis of the result of the preliminary study in Part 1. The purpose of this study is to clarify in detail the relationship between the temporary threshold shift (=TTS) of vibratory sensation and the frequency and severity of exposed vibration.<br>In this case, six subjects, all healthy students, were exposed to localized vibration, which frequencies and levels of acceleration referred to exposure boundary of ISO (1973) (Table 1).<br>In this paper, vibratory sensation threshold was expressed with peak value of acceleration and exposed vibration with peak value of acceleration, velocity or amplitude.<br>The result was as follows:<br>1. TTS of vibratory sensation, immediately after vibration exposure of equal velocity level, showed maximum values at 250Hz exposure and smooth curves from 8Hz to 1, 000Hz exposure. On the vibration exposure of the same frequency, the greater the intensity of vibration was, the greater TTS of vibratory sensation was (Fig. 1).<br>2. On the unexposed side, some TTS of 125Hz and 250Hz vibratory sensation were statisticaly significant (Fig. 2).<br>3. The changes of skin temperature owing to vibration exposure showed similar pattern on the exposed side and the unexposed side. So fine were the changes that they were not significant immediately after vibration exposure but significant 6min. after, by the analysis of variance on the both sides (Fig. 1-4, 2-4, 3-4, 4-4). And it was considered that the effect of the skin temperature on the vibratory sensation threshold was negligible, because the average values of skin temperature ranged from 30°C to 35°C.<br>4. The prediction equations for TTS of vibratory sensation are shown in (Table 2, Fig. 5). The values of TTS of vibratory sensation measured in Part 1 were in reasonably good agreement with the predicted values by these equations (Fig. 6). Therefore, it was considered that these prediction equations have similarity under the condition of this experiment.<br>5. Equal TTS curves were compared with exposure boundary of ISO (1973) (Fig. 5-2, Fig. 7).<br>As the result, both characteristic curves were similar to each other at the frequencies from 63Hz to 500Hz, while different at the higher and lower frequencies. About this difference, it was discussed that Pacinian corpuscle, which is conceibable to be the receptor of vibratory sensation threshold measured in this experiment, has less sensitivity in these lower frequencies and that there would be room for further study in exposure boundary of ISO in that higher frequencies.<br>And it was considered that 30min. level of exposure boundary of ISO was equivalent to TTS of 12.5-15dB on the 63Hz vibratory sensation, 17.5-22.5dB on the 125Hz and 22.5-27.5dB on the 250Hz. Eight-hour level of exposure boundary of ISO was equivalent to TTS of 5dB, 7.5dB and 10-12.5dB, respectively.