The relationship between the hemostatic system and the severity of toxemia was studied in 78 pregnant women with toxemia. The activities of plasma antithrombin III (AT-III), prekaUikrein, plasminogen, Α2-plasmin inhibitor and factor XIII were determined using the chromogenic substrate and fluorescent methods. The antigens of both AT-III and factor XIII were determined by the single radial immunodiffusion method. Plasma bradykinin was determined by radioimmunoassay. The main results obtained were as follows. Both activities of AT-III and plasma prekaUikrein decreased as the gestosis index increased (p < 0.001), and a significant negative correlation was observed between the total score of the gestosis index and AT-III (r = -0.447, p < 0.005) or plasma prekaUikrein (r = -0.434, p < 0.005). The levels of plasminogen, Α2-plasmin inhibitor and factor XIII decreased and plasma bradykinin increased in toxemia. Among the various factors, plasma AT-III and prekaUikrein were the most sensitive indicators of the severity of toxemia.