The authors present their own experience (1980-1985) in the application (im. so called "monotone rhythm and doses") of Prostin 15-M (Upjohn) in legal abortions in the second trimester (14th-20th gestational weeks). This preparation was applied in 470 patients divided into 3 groups for the purpose of differential treatment and analysis: A--gravidae juvenae 13-18 years of age, B--gravidae adultae (19-40 years of age) C--gravidae vetustae 41-46 years of age. The mean age of patients by age groups was: A-16 years + 8 months; B-26 years + 3 months; C-42 years + 7 months. Indications for abortion were: medical in 53.83%, eugenic in 30.21%, medico-social in 14.25%, and ethico-legal in 1.70%. The percentage of primigravidae was 40.42 and of multigravidae 59.76%. The average length of the abortion interval and the average dose of Prostin 15-M (in ml) were as follows: group A 28 h 30' and 8.92 ml; group B 23 h 23' and 8.23 ml. and group C 16 h and 4.97 ml. All recorded side-effects and complications were analysed. Significant complications occurred in 5 cases (1.06%): cervical rupture in 3 cases and massive postabortal haemorrhage in 2 cases. No deaths occurred. The authors elaborated a system of the differential evaluation of the efficacy of this method and its advantages over other methods previously applied. The method has proved to be very simple, efficacious, suitable from the medico-clinical point of view, with a relatively low percentage of complications, and economical (costs of treatment and hospitalisation).