The present study was made to evaluate the efficiency of intraamiotically administered prostaglandin F2alpha upon unselected consecutive patients, hospitalized for legal abortion after the 12th week of pregnancy. In the first series, 178 cases were studied and in these the initial dose was related to the size of the uterus, i. e. 25 mg at 13 weeks, up to 40 mg at 24 weeks. A repeat injection of the same dose was required in 21% of the cases. Abortion occurred in 53% within 24 hours and in 81% within 48 hours. The mean abortion time was 32.3 hours. No failures occurred. In the second series, 73 patients were given an initial standardized dose of 40 mg irrespective of the size of the uterus. A repeat injection of 40 mg was given in 11%. Abortion occurred in 67% of the cases within 24 hours and in 80% within 48 hours. Four cases (5%) were failures. The mean time until expulsion of the fetus was 24.3 hours. Side effects in the form of vomiting and/or diarrhoea occurred about 2 times per patient in both series. In 20-30% a blood loss was sustained of more than 500 ml. Rupture of the cervix occurred in 3 cases. In both series multigravidae aborted faster than primigravidae. Early rupture of the membranes before the cervix was effaced caused very long abortion times in several cases.