PIP: 1030 patients were studied in 1 of the largest single center prospective random trials which assessed the effects of 2 prostaglandin (PG) vaginal pessaries on cervical dilatation and compliance during 1st trimester abortion by uterine aspiration under general anesthesia. Gemeprost 1 mg pessaries inserted 1-4 hours prior to surgery produced marginally greater cervical dilatation and less operative blood loss than PGE2 10 mg pessaries with a reduction in distressing preoperative side effects. No reduction in effect on the cervix was ascertained if pessaries were inserted for only 1-2 hours as compared with 3-4 hours. Postoperative side effects and later complications were infrequent and similar with both preparations. Gemeprost 1 mg pessaries are thus preferable to PGE2 10 mg pessaries for this purpose.