The mechanism of increased nocturnal urine production in adult patients complaining of nocturia has seldom been reported. The objective of this clinical study is to investigate the circadian rhythm of both urine production and plasma arginine-vasopressin (AVP) level, and the efficacy of intranasal instillation of 1-deamino-8-D-arginine-vasopressin (DDAVP) in adult patients complaining of nocturia. Eight patients (seven men, one woman) who ranged in age from 44 to 77 years (mean 64.1 years) were examined. Three of them suffered from Shy-Drager syndrome, and no patient had shown any improvement of symptoms in spite of administration of anti-cholinergic agents and restriction of water intake. Nocturnal urine volume was more than bladder capacity in all patients, and no patient showed normal elevation of nocturnal plasma AVP level. Intranasal administration of DDAVP of 5 or 10 micrograms revealed marked decrease in nocturia, and nocturnal urine volume (p < 0.01). There were mild side effects (headache, nasal obstruction, and hyponatremia) not requiring any treatment. In conclusion, DDAVP is a safe and effective treatment for adult patients complaining of nocturia due to hyperproduction of nocturnal urine and inappropriate nocturnal secretion of AVP.