Abstract : We have studied the effect of a prostaglandin E2 analogue (enprostil), on intragastric acidity, gastric acid and pepsin outputs during a 24 hour period in nine patients with duodenal ulcer in remission. Enprostil 35 micrograms bd dose inhibited 24 hour intragastric acidity by 38% and a 70 micrograms nocturnal dose by 33%. Decrease in nocturnal pepsin secretion was both volume and concentration related.