The optimal physical prophylaxis for deep vein thrombosis is to ride a "bed bicycle" with elevated legs and elastic stockings, when lying in bed. The venous velocities achieved in legs and pelvis are 3--4 times faster than those evoked by walking, the method usually used. The incidence of thrombosis (125I fibrinogen test) up to the 5th postoperative day was 7.7%; in the control group, 38.5%. In patients who were weak, paralyzed, unconscious, relaxed, or with one leg, we obtained with "motor cycle" exercises the same success. The frequency of pulmonary embolism (autopsy findings) was reduced from 2.5 to 0.2%.