Patients who had undergone proctocolectomy and ileostomy for ulcerative colitis have been studied. One group (contrast group) had undergone resection of only small amounts of terminal ileum (median = 4 cm), the other group of patients (study group) had undergone resection of greater lengths of small bowel (median = 60 cm). Gastric emptying and transit of a standard meal through the small bowel were estimated, whilst the amounts of fat, nitrogen, glucose, sodium and potassium excreted by the ileostomy were simultaneously determined. Significantly greater amounts of fat, nitrogen, sodium, potassium and water were excreted by patients who had undergone resection compared with contrast patients (P less than 0.01). The rate of gastric emptying was not increased in patients who had undergone ileal resection compared with contrast patients but small bowel transit within 4 hours of ingestion of the meal was significantly faster. A significant correlation between transit times and excretion of fat was also noted in patients (P less than 0.02). Thus, quite modest ileal resection in addition to proctocolectomy leads to rapid small bowel transit and marked malabsorption of nutrients as well as water and electrolytes.