Objective To compare the effectiveness of gemeprost and misoprostol as prostaglandins used in combination with mifepristone for induction of mid-trimester termination. Design Randomised trial.Setting Scottish teaching hospital.Sample One hundred women undergoing abortion between 12 and 20 weeks.Methods Each woman received 200 mg mifepristone and 36-48 hours later either 1 mg gemeprost vaginal pessary every 6 hours for 18 hours or 4 Â 200 Ag misoprostol tablets vaginally followed by 2 Â 200 Ag misoprostol tablets orally every 3 hours for 12 hours. Success was defined as the percentage of women aborted within 24 hours of the first administration of prostaglandin. Main outcome measures Prostaglandin -abortion interval and side effects.Results There were no significant differences in median prostaglandin -abortion interval between gemeprost (6.6 hours 95% CI 6.0-10.7) and misoprostol (6.1 hours 95% CI 5.5-7.5) ( P ¼ 0.22). The cumulative abortion rates at 24 hours (96% vs 94%, respectively), the surgical evacuation rates (12% and 10%) and the incidence of vomiting, diarrhoea and pain were similar. Conclusion Two hundred milligrammes of mifepristone followed 36 -48 hours later by either vaginal gemeprost or misoprostol is a highly effective way of inducing abortion in the second trimester of pregnancy.