The authors measured the venous pressure in the iliofemoral segment in 12 patients in good general conditions, with a normal patency of the inferior caval vein, profound pelvic veins, and lower limb veins. Examination was performed with Claudy manometer. The resting venous pressure in the external iliac vein was 40--75 mm H2O = 3--5.5 mmHg. During Valsalva's manoeuvre the patients achieved an overpressure 250--1 100 mm H2O = 18--81 mmHg for 20 s. After induction of general anaesthesia and intubation, the anaesthesiologist produced an overpressure of 50 cm H2O in the patient's respiratory circuit for 20 s, but the venous pressure rose only to 90--175 mm H2O = 7-- mmHg. This rise is lesser with a high statistical significance than the overpressure produced in the Valsalva's manoeuvre. In the light of these results the authors discuss the tactics of venous thrombectomy. As a safe prevention of peroperative uplmonary embolism they regard either Valsalva's manoeuvre, carried out under local anaesthesia, or a tourniquet fixation of the clot head during the surgical intervention under general anaesthesia. The anaesthesiologist cannot prevent embolism by restriction of the venous return by producing an overpressure in the respiratory circuit of a patient under general anaesthesia.