Three different regimens for termination of early pregnancy by medical means were compared to vacuum aspiration. Women seeking therapeutic abortion of pregnancy (less than or equal to 56 days amenorrhoea) were allocated to one of four treatment groups: (1) vacuum aspiration (n = 28); (2) 1 mg vaginal pessary of a prostaglandin analogue (gemeprost) every 3 h for up to 5 pessaries (n = 30); (3) the antigestogen (RU 486--mefipristone) 150 mg per day for 4 days by mouth (n = 20); (4) RU 486 in the same dose as group 3 together with 1 mg gemeprost on day 3 (n = 19). Complete abortion occurred more often in women treated with vacuum aspiration (96%), gemeprost alone (97%) and RU 486 plus gemeprost (95%) than in those treated with RU 486 alone (60%). In women receiving up to five gemeprost pessaries alone vomiting occurred in 7 (23%) and diarrhoea in 10 (33%); 16 (53%) required parenteral opiates for relief of pain. Side-effects and analgesic requirements were much reduced in the women who received RU 486 alone or in combination with a single gemeprost pessary. There was no difference in the number of days of vaginal bleeding after abortion between the four groups although there was wide individual variation (mean 10 days, range 1-34). These results confirm that medical induction of abortion in early pregnancy with prostaglandin vaginal pessaries is as effective as vacuum aspiration and that the dose can be reduced five-fold without loss of efficacy when used in combination with RU 486.