Twenty patients, submitted to internal arteriovenous fistula procedure, were randomly assigned to one of the following treatments: defibrotide 400 mg b.i.d. IM (starting the day before surgery and continuing for the following 7 days); calcium heparin 5,000 IU t.i.d. SC (since the day of surgery and for the following 7 days). No deep venous thrombosis or thrombosis of the fistula were noticed during both treatments and no side effects were observed. In the defibrotide group, ELT showed a significant decrease (-40%) attesting an improvement of fibrinolysis without a plasminogen abatement. These findings indicate that defibrotide represent an effective alternative to calcium heparin for antithrombotic prophylaxis of A-V fistula in uremic patients.