It is well established that abortion can be induced successfully in midtrimester of pregnancy by gemeprost vaginal pessaries. A randomised study was carried out to determine the efficacy of mifepristone and dilapan in combination with gemeprost for second trimester termination between 12-18 weeks' gestation. A contemporary group of women treated with gemeprost alone was used as a control group. A single course of 4 x 1 mg gemeprost pessaries was administered every six hours. If abortion had not occurred after 24 hours, a further course of 5 x 1 mg pessaries was administered every three hours over the next 24 hours. In the first twenty hours after administration of gemeprost, 95%, 85% and 72% of women aborted in the mifepristone, dilapan and the control group, respectively. The median induction-abortion interval in the mifepristone group (6.6h) was significantly shorter than the other two groups and fewer pessaries were required to induce abortion. The incidence of diarrhoea and vomiting was lower in the mifepristone than the other two study groups. This study demonstrated the efficacy of mifepristone in combination with gemeprost and this regimen is associated with fewer gastrointestinal side effects.