Enprostil is a synthetic dehydro-prostaglandin E2 with gastroduodenal ulcer-healing and mucosal-protective properties. One hundred and three healthy volunteers were randomized to receive capsules of enprostil 35 micrograms b.d. (the clinically recommended dose), enprostil 70 micrograms b.d., or placebo b.d. All underwent endoscopic assessment of the gastroduodenal mucosa, scored using a 0-4 scale, at baseline and on Days 3, 7, 14, 21 and 28 of dosing. Mean and median maximum scores demonstrated a dose response, and the mean maximum scores were statistically significantly higher for both enprostil groups on each endoscopy day when compared with placebo. The majority of enprostil-treated subjects had petechial haemorrhages. The proportion of volunteers with small white-based mucosal breaks (erosions) was significantly higher for the fundus in the enprostil 70-microgram group on Days 21 and 28 when compared with placebo, but there were no significant differences between treatment groups for any area on the other study days. The 70-microgram dose was associated with significantly more gastrointestinal adverse events than the 35-microgram dose, which was similar to placebo. There were no significant differences between groups for large white-based mucosal breaks (ulcers). We conclude that oral enprostil produced gastric mucosal petechial haemorrhages, primarily in the fundus of the stomach. Gastric mucosal petechial haemorrhages are probably without clinical significance because they are very common in the general population (10-15%) and do not progress to erosions and ulcers.