In our previous reports we hypothesized that both vertigo and deafness in Meniere's disease could be explained by high potassium levels in the scala tympani, not in the scala vestibuli. High potassium levels in the scala tympani may be caused mainly by the increased diffusion of potassium through the distended Reissner's membrane. A relative decrease in the perilymphatic space due to endolymphatic hydrops might also play an important role in the elevation of potassium levels in the scala tympani. Thus, the aggravation of vertigo and deafness is closely linked to the degree of hydrops.In Meniere's disease, vertigo and deafness is often induced by stress. Stress is well known to promote the release of vasopressin, resulting in an increase in plasma vasopressin. We previously reported that an increase in plasma vasopressin was observed in Meniere's disease. Although histological and surgical findings support the hypothesis that the dysfunction of the endolymphatic sac is one of the important factors in Meniere's disease, we speculated that a high concentration of plasma vasopressin may be the other causative factor in the formation of endolymphatic hydrops.