Two series of midtrimester abortion inductions are compared. In one series of 68 cases of midtrimester pregnancies (12-24 weeks), legal abortion was induced by one intraamniotic injection of 2.5 mg 15-methyl prostaglandin F 2alpha. Fetus was expelled in 67 cases (98.5%) after a mean time of 18.4 hours. One case with duplex failed to abort (1.5%). Abortion was complete in 54% of the aborted cases. In the second series of 93 cases abortion was induced by intramuscular injection of 300 microgram 15-methyl PGF 2alpha every third hour (the first dose was 200 microgram) during 30 hours. Fetus was expelled in 79 cases (85%) after a mean time of 16.7 hours. Failure occurred in 14 cases (15%). Abortion was complete in 57% of the aborted cases. Side effects (vomiting and diarrhea) were more frequent in the intramuscular series and very inconvenient to many of the patients. Excessive bleeding occurred more often in the intraamniotic series. A small rupture of the cervix was noted once (primigravida) in the intramuscular group. It is concluded that the intramuscular way of administration is a simple method of second trimester pregnancy termination with small bleedings but that otherwise it is inferior to the intraamniotic route.