To determine the recovery time from noise-induced temporary threshold shift (TTS), a prospective field study was conducted at three worksites where workers are known to be exposed high level of noise. Subjects were selected according to answers on a questionnaire which inquired about otological history and previous noise exposure, including avocational, military and occupational exposures. After excluding employees with past otologic problems, recent exposure to high level noise, and under medications, total 92 employees participated in the study. Among 92 participants, complete consecutive audiometric examinations were carried out at 0~2 hours, 5~7 hours, 14~16 hours after worktime noise exposure on 26 participants wearing hearing protectors and 22 participants wearing no protective devices. The difference between the hearing level 0~2 hours after noise exposure and 5~7 hours is statistically significant by paired t-test(p<0.01). The median recovery times calculated from the data of 22 participants wearing no protective hearing devices are 15.6 hours at 4000 Hz, and 7.7 hours, 10.3 hours, 8.4 hours at 1000 Hz, 2000 Hz and 8000 Hz respectively. These data suggest that when measuring the pure tone audiometry for noise exposed workers, at least 16 hours noise-free interval is required.