The authors investigated the diagnostic value of the recruitment phenomenon with SISI test in normal and various hearing loss. The subjects were 84 ears of normal hearer, 108 ears of chronic otitis media, 14 ears of conductive hearing loss, 81 ears of sensorineural hearing loss and 52 ears of noise-induced hearing loss. The SISI test was applied by Jerger's method of that carrier tone was introduced into the patient's ear at a sensation level of 20 dB. Every 5 sec a short increment is superimposed with 1 dB increment for 200 msec. 20 increments are introduced and subject is required to indicate when he has heard each increment. The SISI score is derived by determing the number of correct identifications of 1 dB increment out of 20 presentations. This procedure was applied at the frequencies of 1 KHz and 4 KHz for each subject ear. We consider that SISI scores of 70-100% was as positive, 25-65% as questionable and 1-20% as negative category. The results were obtained as follows : 1) In majority of normal hearing, 3 dB increment was identified, however 0.6 dB increment was not identified. 2) Recruitment positive rate by SISI test in normal hearing was 8.3%(7 ears) at 1 KHz and 16.7%(14 ears) at 4 KHz. 3) SISI test positive rate in chronic otitis media was 12.0%(13 ears) at 1 KHz and 42.6%(46 ears) at 4 KHz. With this result we considered that middle ear inflammation influences on the inner ear. 4) There was no recruitment positive of SISI test in case of conductive hearing loss. 5) SISI test positive rate in sensorineural hearing loss was 50.6%(41 ears) at 1 KHz and 64.2%(52 ears) at 4 KHz. 6) SISI test positive rate in noise-induced hearing loss was 92.3%(48 ears) at 4 KHz only. 7) These results indicated that SISI test is a useful differential diagnostic method for the cochlear and retrocochlear hearing loss.