Misoprostol is an analogue of prostaglandin E1 and is the first synthetic prostaglandin analogue to be made available for the treatment of peptic ulcer disease. It inhibits gastric acid secretion in man, and there is also some evidence that it limits the extent of gastrointestinal damage induced by ulcerogenic agents in animals and healthy volunteers at doses lower than those required to inhibit acid secretion. This 'cytoprotective' activity has been explained by several mechanisms, but its contribution to the clinical efficacy of misoprostol in healing established ulcers is doubtful since the drug does not appear to be effective in healing peptic ulcers at non-antisecretory dosages. In clinical trials, ulcer healing has been reported in 60 to 85% of patients with duodenal ulcers and 32 to 54% with gastric ulcers receiving misoprostol 200 micrograms 4 times daily for 4 weeks--the recommended dosage. In comparative studies, the percentage of patients with healed ulcers after misoprostol (800 micrograms daily) was not significantly different from that with cimetidine (1200 mg daily), although there was greater pain relief with cimetidine. No study has yet been published concerning the use of misoprostol as maintenance therapy for the prevention of ulcer recurrence, and no long term tolerability data are available. However, in acute ulcer healing studies (2 to 12 weeks in duration) misoprostol has been well tolerated. Diarrhoea was the most commonly reported symptom, and this was only rarely of sufficient severity to interfere with treatment. No evidence of histopathological changes in the gastric mucosa induced by misoprostol have been reported in man. Evidence of uterine stimulant effects in women receiving misoprostol during the first trimester of pregnancy has resulted in the drug being contraindicated during pregnancy. Thus, misoprostol is a new type of antiulcer drug, providing an alternative approach to the therapy of peptic ulcer disease. It has been shown to be effective and well tolerated in the healing of both gastric and duodenal ulcers. Future studies need to identify the specific types of patients likely to obtain most benefit from treatment, in order to define more clearly the place of misoprostol in the treatment of these indications, as well as addressing the possibility of ulcer prevention with lower doses of misoprostol.