Nonopacified lower extremity vein bypass grafts may not be thrombosed. Catheterization of these grafts should be performed whenever possible. If graft patency is demonstrated, vein graft angioplasty may restore flow without fibrinolytic therapy. In two cases of nonthrombosed nonopacified grafts, graft patency was demonstrated by catheterization of the grafts, and normal blood flow was restored by percutaneous transluminal angioplasty.