Desmopressin urine concentration testFormerly intramuscular injection of vasopressin tannate in oil provided a useful and convenient means of assessing urine concentrating ability,' although it was a less potent stimulus than fluid deprivation.'Because vasopressin tannate in oil is now no longer manufactured another practical test of concentrating ability must be defined.We describe an investigation of the use of 1-diamino,8-D-arginine vaso- pressin, desmopressin (DDAVP, Ferring Pharmaceuticals Ltd), by intramuscular (IM) and intranasal (IN) administration to test urine concentrating ability in adults, firstly in an overnight test and then in a shorter day test using only IN desmopressin.The desmopressin day test is simpler and as useful as the conventional overnight vaso- pressin test.