Twenty-two patients who underwent anatomic correction of transposition of the great arteries at the arterial level at the age of 8 weeks to 14 years were reinvestigated 1-4.6 years (mean 2.0 years) after operation. A Dacron tube was used to bridge the gap between the proximal pulmonary route and the distal pulmonary artery in four patients and a tube made of homologous dura mater (2.5 cm in diameter) was used in 18. The nonvalved conduit was placed on the right side of the ascending aorta in nine patients and on the left side in 13. Supravalvular pulmonary stenosis with a gradient of 45-95 mm Hg was found in three patients, all of whom had had the conduit placed on the right side. There was normal growth of the pulmonary artery proximal and distal to the stenotic area. Operation for the relief of the stenosis with insertion of a pericardial patch across the stenosed area was performed in two patients. We conclude that supravalvular pulmonary stenosis after anatomic correction of transposition of the great arteries occurs only when the new pulmonary artery is placed on the right side of the ascending aorta and that the use of a large tube of dura mater appears to allow for rapid growth in early life.