Various asymmetric organic anions have been shown to possess the important capacity to enhance the endogenous fibrinolytic activity in human plasma in vitro. Their further development may well permit induction with them of the thrombolytic activity in human blood in vivo resulting in intravascular clot (thrombi, emboli) dissolution (thrombolysis) by the body’s own fibrinolytic system alone, without the necessity for use of extensive enzyme preparations, which have various drawbacks. The reasons for this statement are as follows: Streptokinase, a plasminogen activator produced by alpha-hemolytic streptococci, which is being used therapeutically as a thrombolytic agent, is a protein that is foreign to the body. Among other disadvantages, its application is restricted because it induces the appearance of antibodies, thus limiting its use in the individual patient. Urokinase as a human plasminogen activator is also currently being used clinically for thrombolytic therapy, although the cost of this treatment is exceedingly high. Urokinase, however, and this is the decisive point, is not identical with the plasminogen activator occurring in the human blood, namely the vascular activator. The differences between these two plasminogen activators have been clearly demonstrated by various investigators; the molecular weights of the two activators are different (Aoki and von Kaulla, 1971; Aoki, 1974). Antisera against urokinase do not react with vascular activator (Kucinski et al., 1968; Aoki and von Kaulla, 1971). These two plasminogen activators hydrolyze acetylglycine lysine methyl ester with different kinetics and have a different stability in salt solution.