15-methyl PGF2alpha methyl ester in a slow releasing vaginal device was administered to 30 women in the first and second trimester of gestation. Ten women were early pregnant (31-49 days following the last menstrual period) and the remaining 20 patients in the 10th to 20th week of gestation. The first group received either a device containing 10 mg 0.5% 15-methyl PGF2alpha methyl ester or a half of that device and the second group either a 0.5% or 1% device. The results were compared with those found following repeated vaginal administration of triglycerides suppositories, containing 15-methyl PGF2alpha methyl ester, to 50 early pregnant patients and 30 patients in the second trimester of gestation. The mean total dose of the compound given to these two groups was 3.9 and 7.8 mg respectively. All the 60 early pregnant patients aborted following treatment judged from clinical course and decreasing HCG values. Bleeding started as a rule three to six hours following the start of treatment and continued for 10 to 14 days. In two patients the abortion was incomplete. The side effects in the patients who received half the 0.5% device was comparable to those following the repeated vaginal suppositories while in the patients who obtained the whole 0.5% device, the frequency of side effects was increased indicating that an unnecessary high dose was given. In all the three groups of patients in the late first and second trimester of pregnancy, treatment resulted in abortion within 24 hours in 90% of the patients. In the 1% device an accumulation of side effects was found during the first hours following the start of treatment probably due to an initial, more rapid absorption of 15-methyl PGF2alpha methyl ester. With the repeated administration and with the 0.5% device, the side effects occurred mainly in the hours prior to abortion. However, in all three groups of patients the side effects were within acceptable levels. These preliminary results indicate that further development on the device may result in an effective one vaginal administration treatment for termination of both first and second trimester pregnancies.