A model of venous thrombosis on the rabbit marginal ear vein was developed. It is based on occlusion of a segment of the left or right ear vein followed by injection of thrombin into this segment. Thrombolytic activity of longolytin applied externally onto the thrombotic venous segment was evaluated. The drug 2-fold shortened the time of clot lysis and 4–4.5-fold increased the rate of thrombolysis. The effect of longolytin was potentiated by heparin. The rate of lysis was higher in large thrombi and in the left vein (effect of asymmetry).