Six patients, aged 8 to 20 years, with valved right ventricle to pulmonary artery conduits were catheterized for balloon dilation valvuloplasty of stenotic and calcified bioprosthetic valves. Conduit stenosis was severe in all cases, with peak-to-peak systolic pressure gradients of 62 to 100 mm Hg (mean 79 mm Hg) and right ventricular systolic pressures of 87 to 115 mm Hg (mean 100 mm Hg). Three patients had good results, with residual peak-to-peak systolic pressure gradients of 20, 25, and 35 mm Hg. In two other patients, repeated balloon rupture before full inflation occurred, and residual gradients were high (55 and 60 mm Hg). One patient had substantial proximal and distal conduit obstruction in addition to valvular stenosis, and balloon dilation valvuloplasty was not attempted. No complications occurred in five patients; one patient required iliac vein exploration to remove an avulsed balloon fragment. Balloon dilation valvuloplasty can relieve bioprosthetic valve stenosis and postpone conduit replacement in some patients.