The effectiveness of 19 modified Blalock-Taussig shunts performed with expanded polytetrafluoroethylene was evaluated clinically and by cardiac catheterization with angiography 4 to 24 months after operation. Fifteen patients underwent operation in infancy. Conduit diameters included 4 mm (nine cases), 5 mm (eight cases), and 6 mm (two cases) sizes. Two of the 4 mm conduits failed after 1 year following implantation. The remaining 17 shunts (89%) remained widely patent. In patients with patent shunts, the oxygen saturation values were significantly improved from the preoperative values. Two children demonstrated associated subclavian artery occlusion distal to the graft anastomosis. There were no deaths. Thirteen children underwent more complete elective cardiac repair 5 to 24 months later. Although the modified Blalock-Taussig procedure is an effective short-term alternative to the classic Blalock-Taussig shunt, the effectiveness of the 4 mm diameter conduit may be limited without postoperative anticoagulant therapy.