Fluctuation of hearing at low frequencies is one of the most characteristic findings in Meniere's disease and seems to be a phenomenon closely related to changes of endolymphatic pressure and volume. In the present study, pressure was applied to the external auditory canal of patients with Meniere's disease, and the effect on the bone conduction threshold was examined at times of depressed and improved hearing. In more than half of these cases, it was found that the pressure effect was marked at the time of improved hearing acuity, but not at the time of depressed hearing. This effect was also confirmed in more objective experiments with guinea pigs. It is concluded that the fluctuation of hearing in Meniere's disease seems to be a phenomenon accompanying the endolymphatic pressure change in the scala media.