An elevation of the plasma arginine vasopressin (AVP) level has frequently been observed in Meniere's disease patients. However, little is known regarding the mechanism behind this elevation. The plasma AVP levels in acute phase were determined in 21 Meniere's disease patients and 16 patients with other types of vertigo. The plasma AVP levels of Meniere's disease patients in the acute phase were significantly higher than in those of other vertigo patients (p < 0.01). In Meniere's disease patients with abnormally high levels of AVP (more than 3.5 pg/ml) in the acute phase, 36% of patients were resistant to conservative treatments for frequent vertigo attacks for the follow-up period of at least 2years. A significant correlation was observed between the plasma AVP in the acute phase and the highest hearing threshold level at a frequency of 1kHz for the follow-up period of at least 1 year (r=0.45, p < 0.05). These results suggest that the elevation in plasma AVP level in the acute phase is associated with the prognosis of Meniere's disease.