The treatment of thrombophlebitis in pregnancy with streptokinase is reviewed. Four personal cases are reported. In 3 cases the streptokinase treatment of thrombosis was carried out in the first trimester of pregnancy. Two pregnancies ended in spontaneous term deliveries of well infants without malformations. In one case the pregnancy ended by a spontaneous abortion two weeks following the treatment of the thrombosis. It is suggested that the abortion was much more likely due to a severe state of shock with pulmonary embolism following laparotomy in early pregnancy. The authors are of the opinion that the thrombolytic therapy with streptokinase should also be carried out in the first trimester of pregnancy to prevent embolization of thrombotic material and to prevent a post-thrombotic syndrome. In each case, streptokinase treatment should be followed up with subcutaneous prophylactic treatment with Heparin until term to prevent recurrent thrombophlebitis in pregnancy. With the onset of labour Heparin medication should be interrupted and the thrombin time should be normal with the beginning of the second stage of labour or the Heparin effect should be neutralized by protamine chloride. At the earliest six hours postpartum, the subcutaneous Heparin prophylaxis can be resumed in order to prevent recurrent thrombo-embolism during the postpartum stay.