The vasopressin analogue, 1-desamino-8-arginine vasopressin (desmopressin), is a potent antidiuretic without the pressor effects of vasopressin. A total of 18 patients with acute renal colic due to stone disease received 40 microgramsf1p4mopressin intranasal spray with encouraging results. There was a significant decrease in the colic pain intensity from an initial mean visual analogue score of 67 +/- 17 mm. to 39 +/- 36 mm. within 30 minutes (p < 0.001). Eight patients (44.4%) had complete pain relief within 30 minutes of administering intranasal desmopressin spray. Nine of 10 patients who required intramuscular diclofenac sodium achieved complete pain relief within another 30 minutes. In other words, when intranasal desmopressin spray was administered before diclofenac sodium, 94.4% of the patients achieved complete pain relief and were discharged home. The mechanism of analgesic action of desmopressin in renal colic is uncertain. At the peripheral level, desmopressin may alleviate the acute renal colic through its potent antidiuretic effect or by relaxing the renal pelvic and ureteral smooth muscles. The central analgesic effect of desmopressin by stimulating the release of the hypothalamic beta-endorphin is proposed. We conclude that intranasal desmopressin spray can be used successfully in the treatment of renal colic. It may also replace prostaglandin synthetase inhibitors in treating renal colic with the advantage of avoiding the potential side effects. Further studies are needed to investigate whether the combination of desmopressin with analgesics or spasmolytic drugs offers competitive results compared with those achieved by prostaglandin synthetase inhibitors in the treatment of renal colic.