The glycerol test described by Klockhoff and Lindblom in 1966 has been used as tool for the diagnosis of endolymphatic hydrops. However, the exact effect of glycerol on inner ear function is unclear. In this investigation of possible changes in hearing after glycerol intake, pure tone thresholds were measured before and 1, 2 and 3 hour after glycerol intake in 50 normal subjects. Pure tone thresholds were also measured in 25 normal subjects with normal saline intake as controls. Analysis of the hearing threshold at each frequency tested(0.125 to 8KHz), revealed that threshold improvement was greatest in the low and middle frequency range. This study reveals that hearing changes after glycerol intake can be demonstrated in normal subjects. The following results were obtained ; 1) The cases of hearing improvement were 21 ears(21.4%) in glycerol intake group and 3 ears(6.0%) in control group(P<0.05). 2) The cases of positive reaction on time course were 6 ear(6.1%), 11 ears(11.2%) and 15 ears(15.3%) in glycerol intake group and 0, 1 ear(2.0%) and 2 ears(4.0%) in control group at each 1,2 and 3 hours. 3) The hearing improvement in glycerol intake group was mainly at low and middle frequency range, especially at 500Hz. 4) The cases of hearing decrement were 5 ears(5.1%) in glycerol intake group and 4 ears(8.0%) in control group. 5) Among the side effects after glycerol intake, nausea was most common and followed by thirst, headache and diarrhea in descending orders.