The objective of this work was to study the abortifacient effects of misoprostol, an orally active prostaglandin E1 (PGE1) analogue, in the second trimester. A randomized study of two prostaglandin regimens in women pre-treated with the antiprogesterone mifepristone was carried out in the gynaecological wards of Aberdeen Royal Hospitals, NHS Trust, and included 60 women at 13-20 weeks' gestation, in whom termination of pregnancy had been agreed. Following pre-treatment with mifepristone 600 mg women were randomly allocated to one of two prostaglandin regimens which started 36-48 h later. The first misoprostol 400 micrograms orally (up to three doses) followed by gemeprost vaginal pessary 1 mg up to two doses. The second was gemeprost vaginal pessary 1 mg up to five doses. The main outcome measures were success rate induction-to-abortion interval and side-effects. There were no significant differences between the two groups in any of the main outcome measures. We conclude that misoprostol is a stable, cheap PGE1 analogue with demonstrable efficacy and acceptable side-effects in the management of second trimester abortion. Further work is needed to establish the optimum dose and regimen.