Within the framework of the multicenter randomized placebo-controlled double-blind clinical trial "VETTER-1" the authors carried out assessment of therapeutic efficacy and safety of oral drug Thrombovasim® possessing a thrombolytic effect in comprehensive treatment of lower-extremity deep vein thrombosis (LEDVT). The clinical study comprised a total of 154 patients. All patients received standard therapy accepted in LEDVT. The patients were subdivided into 4 groups. Patients from the three study groups received Thrombovasim® at a daily dose of 1,600, 3,200, and 4,800 IU. The control group patients were given placebo. Efficacy was assessed by the results of ultrasound duplex scanning first performed before treatment commenced and then after it terminated. The relative frequency of positive dynamics according to the findings of instrumental methods of study in patients taking Thrombovasim® amounted to 0.728 and in the group of patients receiving placebo to 0.585, p=0.0031. Comparing the degree of blood flow normalization in the zone of the compromised blood flow revealed a pronounced dose-dependent effect: in patients taking the drug at a daily dose of 1,600 IU, the relative frequency of positive dynamics amounted to 0.707 corresponding to an increase in therapeutic efficacy by 21%, for a dose of 3,200 IU these parameters amounted to 0.0257 and 24% and for 4,800 IU - 0.747 and 28%, respectively. In patients taking Thrombovasim® there were no cases of negative dynamics observed. Of the patients taking Thrombovasim®, none developed undesirable or severe adverse events. Inclusion of Thrombovasim® into the composition of comprehensive therapy for LEDVT increases efficacy of treatment at the expense of a spontaneous thrombolytic effect. The most effective dose amounted to 4,800 IU daily. Thrombovasim® turned out to be an efficient and safe agent in treatment of venous thromboses.