Polytetrafluoroethylene tubular grafts are useful in performing a systemic-to-pulmonary artery shunt (modified Blalock-Taussig). They allow a controlled-volume shunt, avoid kinking of the pulmonary artery, and preserve distal flow in the subclavian artery. Unfortunately, occasionally excessive serous fluid will drain through the interstices of the fabric. This results in excessive and prolonged chest tube drainage and/or localized seroma formation around the graft. This complication occurred in 26 children, an incidence of 18.8% of the 138 modified Blalock-Taussig operations. Repeat thoracotomy was required in four of these children--for evacuation of seroma mass in three and for relief of cardiac tamponade in one. Four other children required reinsertion of pleural or pericardial chest drains for excessive serous drainage persisting as long as 6 weeks after operation. Wrapping of the graft with silicone sheeting to facilitate subsequent takedown of the shunt led to seroma formation in five of nine children. We believe this practice should be abandoned. Excessive drainage of serous fluid through the interstices of PTFE grafts in almost 20% of our patients has compromised an otherwise satisfactory result of the modified Blalock-Taussig operation.