Bladder dysfunction with increased voiding frequency and incontinence is a common problem in patients with multiple sclerosis (MS). In the present study, the effect of the synthetic vasopressin analogue, desmopressin, was evaluated on the voiding frequency in 26 patients with MS suffering from socially handicapping voidings and incontinence problems during daytime. A two-week run-in observation period to establish normal voiding patterns was followed by a double-blind, placebo-controlled cross-over study with 20 micrograms intranasal desmopressin during daily activities. There was a significant decrease in the number of voidings during the 6-h period after intranasal intake of desmopressin. Side effects were well tolerated and there was no hyponatremia or hypertension registered. Intranasal desmopressin is an efficient and well-tolerated treatment of voiding problems in patients with MS during daily activities.