OBJECTIVE To determine the efficacy of a new regimen of the antiprogestogen mifepristone and gemeprost for midtrimester abortion. METHODS Prospective study. METHODS Medical Termination Unit, Simpson Memorial Maternity Pavilion, Edinburgh. METHODS One hundred women undergoing midtrimester abortion. METHODS Women were pretreated with 200 mg mifepristone 36 h before prostaglandin; 1 mg gemeprost was administered every 6 h for the first 24 h. If abortion had not occurred, 1 mg gemeprost was administered 3 hourly over the next 12 h. RESULTS Ninety-six percent and 99% women aborted within 24 h and 48 h, respectively. The median prostaglandin-abortion interval was significantly shorter in multigravidae compared to primigravida (6.6 vs 8.2 h, P < 0.01). The median number of gemeprost pessaries to induce abortion was only two and 47% of women required one pessary. The incidence of vomiting and diarrhoea was 31% and 5%, respectively. Eighty-four percent of women required intramuscular diamorphine for analgesia. Thirty-three percent of women required an evacuation of the uterus following abortion. CONCLUSIONS The shortened induction-delivery interval following pretreatment with mifepristone makes it possible to conduct midtrimester abortion on a daycare basis.