Ultrasound fibrin clot destruction was investigated in vitro using electron microscopy and by monitoring the changes in the light transmission of clot debris suspension. It has been established that in the course of a combined action of ultrasound and fibrinolytic agent at high ultrasound intensities and short sonification periods, fibrin clot is disrupted mainly due to sonomechanical treatment, while fermentative lysis takes place in parallel and at a significantly lower rate. However, the streptokinase action prevails after ultrasound switching off and results in the prevention of clot debris conglomeration.