Aspirin induces a haemorrhagic diathesis that persists for at least 1 week after discontinuation of the drug. The effect of the vasopressin analogue desmopressin was studied in 12 patients treated with aspirin who were undergoing cholecystectomy. Desmopressin was given to six of these patients. There were five postoperative bleeding complications; all occurred in patients who had not received desmopressin (P < 0.05). The bleeding time was prolonged in aspirin-treated patients and normalized by desmopressin (P < 0.05). Desmopressin can be used safely to prevent bleeding induced by aspirin.