Maximum urine concentration capacity was studied in healthy adults using different routes and doses of administration of 1-deamino-8- d-arginine vasopressin (DDAVP) – desmopressin. Plasma levels of DDAVP showed a dose-dependent increase after the subcutaneous but not after the intranasal administration. The effect on urine osmolality was similar but more prolonged after the subcutaneous as compared to the intranasal route. We conclude that subcutaneous injection is a simple and reliable way of administering DDAVP. A dose of 4 μg in adults is optimum diagnostically and it corresponds to 20–40 μg administered intranasally.