OBJECTIVE: Misoprostol (PGE1) administered per vaginimi, has been reported to reliably effect second trimester uterine evacuation and with fewer maternal side effects than PGE2 vaginal suppositories. Prior reports using PGE1 predominantly included women with a fetal demise. Our intent was to examine the efiicacy of PGF1 for a mid-trimester pregnancy termination in an unselected population. STUDY DESIGN: Eligible, consenting women at 17-24 weeks' gestation admitted for pregnancy termination were randomlv assigned to receive either vaginal PGE1, 200μgq12h or low-dose vaginal PGE., (lOmgqrih) plus intravenous concentrated cmtocin (COP). A cervical ripening agent (laminaria), prophylactic antiemetic, antipyretic and an antidiarrlieal were' routinelv administered. Treatment success was defined as an induciion-lodelivery interval 24 hours. Our sample size calculations indicated that 150 women would be required to detect a 10% difference in success rales (α = .05. β= .2). RESULTS: An interim analysis of the first 30 (15-PGK, 15-COP) women indicated that the groups were matched with regard to gestational age, parity and initial cervical dilatation; 93% of the inductions in the PGK, group and 80% in ihe CO? group were performed ior other than fetal death (p = .6). PGE, was associated with more failures (33% s. 13%. p = .2), a longei induction-deliverv inten'al (22h vs. 18h, p=.09) and a higher rate of retained products requiring curettagc (27% 's. 13 , p = .fio). While these differences were not statistically significant, the livebirth rate associated with PGEj was significanth higher (50% s. f)%, p=.(K)6). Tlie incidence of nausea was identical (47a< ) in both groups, while vomiting (p = .0(i), diarrhea (p= OH) and fever >100.4" (p = .05) were more commonh associated with low-dose P(iE2 phis (-OP. \e estimated that if the current failure rates continued, a sample oi 70 would attain statistical significance (p<.05). CONCLUSIONS: Miioprostol administered as a vaginal tablet in a dose oi'200jig q!2h is not a satisfactory alternative to concentrated oxvtorin plus low-dose vaginal PGE, for midtrimester pregnancy termination.