It has previously been established that the administration of mifepristone prior to prostaglandin-induced second trimester termination of pregnancy significantly reduces the induction to abortion interval. In this study, mifepristone (600 mg) was administered 24, 36 and 48 h prior to extra-amniotic infusion of prostaglandin in an attempt to elucidate the optimal time interval. There was a significant reduction in the induction to abortion interval, dose of prostaglandin required and attendant side effects in all three treated groups compared to controls. However, there was no significant difference among the treatment groups, despite evidence of increased uterine activity 36 h following mifepristone administration. No bleeding was observed prior to prostaglandin infusion in any of the groups and it is suggested that mifepristone could be administered safely prior to hospital admission for termination.