Current techniques for treating chronic venous disease caused by venous valve incompetence all have deficiencies. A need exists for a simple technique to restore competence to the diseased valves at multiple sites in the venous system. The Venocuff is an implantable device developed to restore venous valve competence by reducing the vein circumference. Two animal models are described that are useful in the study of venous valve incompetence; the device was tested in these two models in the jugular vein of sheep. The first model was of naturally incompetent valves. The device was implanted around 11 completely incompetent and seven partially incompetent valves in 18 veins of 11 sheep. After implantation competence was restored or improved in all valves. The second model made use of an arteriovenous fistula to produce incompetence in the jugular vein in four sheep. The implant increased the pressure difference across the valve from 16 to 68 mm Hg. The Venocuff implant was thus effective at restoring valvular competence in the two animal models studied. There is evidence that valvular incompetence in these models and the results observed may be applicable in some cases of chronic venous disease in humans.