We have used a derivative of PGE2, sulprostone, to induce abortion in the second trimester of pregnancy in 26 women. 500 micrograms of sulprostone were administered i.m. every four or six hours and clinical rating of the efficiency of the treatment was done using a scale ranging from 20 to 100. FSH, prolactin, 17-beta-estradiol, progesterone, hPL and beta-hCG plasma levels were monitored during treatment. The drug was effective in 20 cases (79.9%) while in three cases additional administration of oxytocin was necessary and in three cases no effect was seen. Treatment was interrupted, due to the appearance of unpleasant side effects, in only one case. No specific variation in hormone levels was seen. In three cases in which only two doses of the drug were sufficient to induce abortion, hormone levels dropped more rapidly and to a greater extent than in the remaining cases. A correlation exist between the rate of decrease in progesterone and 17-beta-estradiol plasma levels and the time required for the treatment to induce abortion.