In a randomized, endoscopically controlled double-blind trial the effectiveness of a twice daily dose of the prostaglandin E2-analogue enprostil was compared with ranitidine given to 93 ambulatory patients with benign gastric ulcers. Under 35 micrograms b.i.d. enprostil the ulcer healing rates after 2, 4, 6 and 8 weeks averaged 22% (10/46), 58% (26/45), 80% (35/44) and 86% (37/43). The corresponding values for ranitidine 150 mg b.i.d. were 22% (10/46), 66% (29/44), 84% (38/45) and 89% (41/46). The differences were not statistically significant. Both drugs had a similar influence on the ulcer symptoms and were well tolerated. The findings suggest that enprostil can be given in a twice daily dosage in the treatment of benign gastric ulcers.