The effect of the H2-receptor blocking agent cimetidine on jejunal effluent was examined in eight short-bowel patients with high-output jejunostomies. Stool mass and faecal excretion of sodium and potassium were significantly reduced by intravenous injection of 400 mg cimetidine four times a day. The amount of calcium, magnesium, phosphate, zinc, and fat in jejunostomy effluent did not change significantly. Cimetidine may be considered an antidiarrhoeal drug in extensively small-bowel-resected patients with a jejunostomy and may reduce the need for parenteral saline supply in these patients.