The effects of 1-deamino-8-D-arginine vasopressin (DDAVP), 1-deamino-4-valin-8-D-arginine vasopressin (DVDAVP) and 8-arginine vasopressin (AVP) on water metabolism have been examined in 18 patients suffering from central diabetes insipidus. The hormone derivatives were sublingually administered. It was established that DDAVP and DVDAVP significantly reduced diuresis and increased urine osmolarity. DVDAVP was found to be more effective than DDAVP. AVP administered in equal doses had no significant effect on water metabolism. The duration of the action of sublingually administered DDAVP was 12 hrs; after dosing DVDAVP the effect lasted even 6 hrs. During one week of DDAVP administration, the accumulation of the drug was indicated by the gradual decrease of diuresis and the increase of the urine osmolarity. The sublingual administration of both DDAVP and DVDAVP tablets (3 X 30 micrograms/day) had an adequate therapeutic effect.