Abortion was successfully induced by intravaginal administration of a newly developed silastic device impregnated with 15(S)-15-methyl-prostaglandin F2alpha methyl ester in a concentration of 0.5% in 26 of 35 women in the 12th to the 24th weeks of gestation and by prostaglandin with concomitant oxytocin infusion in an additional 5 patients. A second comparable group of 35 women, with gestational ages from 9 to 23 weeks, received a silastic device with a concentration of 1.0% of the prostaglandin. Twenty-six women in the second group aborted with prostaglandin alone and an additional 6 patients aborted with combined prostaglandin-oxytocin therapy. Seven patients of the 70 included in this study failed to abort with intravaginal administration of 15-ME-PGF2alpha methyl ester even with concomitant oxytocin therapy; this group included 4 patients receiving the 0.5% device and 3 patients with the 1.0% device. The mean abortion time for the 31 successful abortions with 0.5% device was 15.15 hours and multiparous patients aborted in a mean time of 9.69 hours, significantly faster than the nulliparous patients, mean time 18.49 hours. The mean abortion time for the 32 successful abortions with the 1.0% device was 15.61 hours and there was no significant difference in the mean abortion times between nulliparous and multiparous patients in this group. No significant difference could be demonstrated between the mean abortion times of patients receiving an 0.5% concentrations of prostaglandin and patients receiving a 1.0% concentration of the drug. In both groups more than 40% of the patients had aborted within 12 hours of the insertion of the prostaglandin device and more than 80% had aborted within 24 hours. The intravaginal device appeared to be effective in inducing abortion throughout the gestational ages tested in this series. Peripheral plasma levels of 15-ME-PGF2alpha were analyzed in 15 patients with the 0.5% device and 8 patients with the 1.0% device. In patients with the 0.5% device the mean plasma concentration of prostaglandin peaked 2 hours after insertion, while in patients with the 1.0% device the peak was achieved within 15 minutes of insertion followed by a rapid decline in plasma prostaglandin levels. Diarrhea was the most frequent side effect related to the intravaginal administration of the prostaglandin, and in this series the severity of this gastro-intestinal disturbance appeared to be significantly higher in patients receiving the 1.0% device.