This study describes changes in diuresis during a two-month treatment with 40 micrograms desmopressin (Minirin) in a group of elderly persons with increased nocturnal diuresis and decreased ADH secretion. The average age of the men (n = 7) was 72 +/- 4 years and of the women (n = 14) 73 +/- 6 years. Nocturnal diuresis decreased after one and two months by 21% and 20% in the men and by 36% and 34% in the women, respectively. Half of the change persisted among the women but not among the men one month after the treatment. The decrease in nocturnal diuresis was greatest among those who, before the treatment, had a large part of their diuresis during the night. Diuresis during the day changed only insignificantly. Body weight did not change during treatment, nor did blood pressure, osmolality, sodium or potassium in serum. Sleep improved during treatment. In one case, side-effects were observed, with a feeling of swelling in the body and decreased diuresis in the morning.