Proctocolectomy (PC) with small bowel resection may lead to profuse ileostomy diarrhoea which can be difficult to treat. The effect of a recently developed long acting somatostatin analogue (SMS 201-995) on ileostomy output was investigated in 5 patients who had undergone PC and ileal resection (median 120 cm) and who suffered severe diarrhoea (4-7 litres/24 h). Gastric emptying, transit of a standard meal through the small bowel and the amounts of nutrients excreted were simultaneously determined during double blind infusion of SMS (25 micrograms/h) and placebo (isotonic saline 125 ml/h). SMS 201-995 significantly reduced ileostomy output (P less than 0.05) and water excretion (P less than 0.05) and prolonged small bowel transit time (P less than 0.05). Whilst having little effect on gastric emptying, or on the excretion of glucose or nitrogen, fat excretion was significantly increased (P less than 0.05). In two patients subcutaneous administration of SMS 201-995 (50 micrograms b.d.) has maintained a reduced ileostomy output for 4 and 6 months respectively.