The present study was designed to evaluate the efficacy of misoprostol (Cytotec) for the healing of gastroduodenal ulcer by double blind clinical trial. Twenty four patients with endoscopically- proven gastric or duodenal ulcer complicating chronic liver disease were randomized to receive misoprostol 200 ug or placebo 4 times a day for 4 weeks. Endoscopic, clinical and laboratory assessments were made before, during and after 4 weeks' treatment. The results were summerized as followitng; 1) After 4 weeks' treatment with misoprostol or placebo, complete healing rates of gastroduodenal ulcer were 36.4%, 0%, respectively and marked improvement (at least 3 endoscopic stages of the ulcer state,) was observed in 72.7%, 15.4%, respectively(p<0.03). 2) One patient treated with misoprostol suffered from mild watery diarrhea, which was transient in spite of continued administration. Another patient complained of mild lower abdominal discomfort. There was no evidence of significant drug-related hepatocellular injury and the precipitation of hepatic failure or encephalopathy by the misoprostol. We conclude that misoprostol 200 ug 4 times a day is effective as well as safe for the healing of gastroduodenal ulcer in patients with chronic liver disease.