Objective: to search for a procedure for drug injection into the pulmonary artery to enhance the efficiency of thrombolytic therapy. Subjects and methods. Twenty patients with submassive unilateral pulmonary thromboembolism were examined. Selective thrombolysis was performed in 10 patients of Group 1. Local thrombolytic therapy (RF patent No. 2376042) was used in 10 patients of Group 2. The authors simulated thrombolysis with a contrast agent and studied pressure in the pulmonary artery in the sites of its bifurcation and a thrombus and the concentration of a fibrinolytic agent at the site of a thrombus and in the cubital vein. Thrombolytic therapy-induced complications were analyzed. Results. Pressure at the site of the pulmonary artery bifurcation was recorded to be, on the average, 6.2±0.9 mm Hg higher than that at the site of the thrombus. Simulation of selective thrombolysis by the contrast agent showed its movement to the area contralateral to the thrombus. Local thrombolysis simulation indicated the spread of the contrast agent along the thrombus and its failure to enter the systemic bloodstream. In local thrombolysis, the concentration of a fibrinolytic agent at the site of the thrombus after administration of a test dose was 930 times greater than that during selective thrombolysis. With local thrombolysis, the peripheral venous concentration of Actilyse was significantly lower than that with selective thrombolysis. During the latter, there were no differences in the Actilyse concentration at the site of the thrombus and in the peripheral vein. Hemorrhagic events were recorded in Group 1 patients. These were absent in Group 2. Conclusion. The findings demonstrate that selective thrombolytic therapy is ineffective. The administered fibrinolytic agent is washed out into the systemic bloodstream, as confirmed by the absence of differences in the concentrations of Actilyse at the site of the thrombus and in the peripheral vein. As compared with selective thrombolysis, local one elevates the concentration of the agent at the site of the thrombus; by spreading along the thrombus, the agent fails to enter the systemic bloodstream, which reduces the number of complications. The efficiency of the method is evidenced by normalization of pulmonary pressure. Key words: local thrombolysis, selective thrombolysis, pulmonary thromboembolism, Actilyse concentration, thrombolysis simulation.