Desmopressin (DDAVP) is used intramuscularly in the treatment of post operative diabetes insipidus as soon as the condition is diagnosed to ensure continuous replacement of antidiuretic hormone secretion during the first 5 days of therapy. Two successive studies, each involving 15 patients, were conducted. The first study was designed to test the effectiveness and detect the possible side effects of intramuscular DDAVP, while the purpose of the second study was to evaluate the clinical application of the drug. With seven 2 mcg doses of DDAVP, administered 12-hourly by intramuscular injection to patients weighing more than 30 kg, continuous antidiuresis during 96 hours was achieved. This method is simple and effective, but it should not be prolonged beyond that period of time. Moreover, to prevent plasma hypo-osmolality, fluid intake must be strictly controlled and kept at the same level as or below diuresis.