The author has investigated the hearing difference between right and left ear in 477 cases of noise deafness who have worked at noisy industrial factories in Busan City and its suburb area. The investigation of the hearing difference was based on the following 4 types of noise deafness. High frequency deafness (H type) was the type in which the hearing loss of air conduction was greater than 20 dB in high frequencies. Speech range deafness (S type) was the type in which the hearing loss of air conduction was greater than 20 dB in middle frequencies. Mild deafness (M type) was the type in which the hearing loss of air conduction was greater than 15 dB and less than 20 dB in low and high frequencies. Both frequency deafness (B type) was the type in which the hearing loss of air conduction was greater than 20 dB in high and middle frequencies. The conclusions obtained were as follows ; 1) The detective rate of hearing difference between right and left in noise deafness was 59.1% showing 282 cases among 477 cases. 2) Hearing difference between right and left was usually established by the first 14 years of work, and after then further hearing difference seemed to the very slight. It might be said that the hearing difference depends on the duration of exposure to noise, the shorter the more and longer the lesser. 3) The difference of hearing level between right and left was 10~19 dB in 107 cases (54.9%), 20~29 dB difference in 51 cases (26.1%), 30~39 dB difference in 22 cases (11.3%) and over 40 dB difference in 15 cases (7.7%). 4) The incidence of different hearing between right and left in each frequencies was 137 cases (51.8%) in high frequency. 36 cases (18.5%) in both high and middle frequencies and 22 cases (11.3%) in middle frequencies. 5) The incidence of different hearing between right and left in each type of noise deafness was seen most frequently in high frequency deafness (H type) and speech range deafness (S type).