An original method was used to isolate polypeptides from citrate platelet-free plasma of healthy subjects. These polypeptides were able to prolong recalcification, kaolin, kaolin-cephalin and prothrombin plasma time, sharply reduce thrombin time of standard and heparinized plasma, to inhibit fibrin self-building and stimulate fibrinolytic activity of blood. An antiheparin effect of polypeptides in adequate doses is similar to that of protamine sulfate. Polypeptide antiheparin plasma factor has molecular mass about 2000 D, its chromatographic profile coincides with that of protamine sulfate.