The risk of Deep Venous Thrombosis (DVT) in the immediate postoperative period varies from 0.8 to 96% of cases depending on major or minor operations and on age of patients. We have employed 8,000 I.U. AXa/daily of LMW-Heparin injected subcutaneously from one day preoperatively and prolonged for 8 days after surgical procedures in 40 patients operated upon by an aorto-femoral bypass in 25 cases, a femoro-popliteal below the knee in 8 and an extra-anatomical bypass in 7. The onset of DVP in the lower limbs was investigated by clinical examination, venous Doppler pressure evaluation, waveform analysis and echotomography and the 125I-Fibrinogen uptake test. There was no intraoperative increased bleeding and the preclotting of the prosthetic grafts was inaffected. A DVT was detected during the second postoperative day, by means of the 125I-Fibrinogen test in the calf of only one patient (1/40-2.5%), submitted to an aorto-bifemoral bypass, in whom the clinical pattern and ultrasound investigations were negative. The single daily subcutaneous administration has never caused side effects in the site of injection and it seems a real improvement in the heparin treatment. These results emphasize the advantage of the use of LMW-Heparins in patients submitted to arterial surgical reconstructions of the lower limbs for the prevention of the DVT.