Animal and clinical evidence suggests that the antiprogestin mifepristone may be of potential use for cervical preparation before surgical termination of pregnancy. A double-blind, multicentre study was undertaken of 230 primigravid women with 10-12 weeks amenorrhoea who were randomly assigned to groups given 0 (placebo), 25, 50 or 100 mg mifepristone twice at 24 and 12 h before vacuum aspiration. In mifepristone-treated women the cervix was on average between 0.9 and 1.2 mm more dilated at operation, but the effect was not dose related. High resistance during further mechanical stretching tended to be encountered more often and at a smaller cervical diameter in the placebo group than in the women given mifepristone, but these differences were not statistically significant. In contrast, the ease of dilatation assessed subjectively by the operating surgeons was not only improved by the antiprogestin, but was also dose related. Mifepristone therapy was not associated with any side-effects and only two of the women from the highest dose group experienced preoperative vaginal bleeding. Peroperative blood loss, post-operative complications, the duration of post-operative bleeding and the interval to the first period were similar in the four treatment groups.