Balloon dilatation valvuloplasty was performed in 16 patients with pulmonary valve stenosis aged 10 days to 17 years. Gradients were reduced in all but two patients and were less than or equal to 20 mm Hg after the procedure in all but these two and one other. Unsatisfactory initial results in these three patients were attributed to the use of too small a balloon in one patient (gradient subsequently abolished at repeat valvuloplasty), to a dysplastic valve in a neonate, and to the fact that there had been a previous surgical valvotomy with scar tissue formation in one patient. The good result was retained in six of seven patients followed up at three to six months. In one the gradient, having been reduced from 60 to 18 mm Hg, had risen to 35 mm Hg. Repeat valvuloplasty was technically impossible in this patient, but in two others residual gradients of 24 and 22 mm Hg were reduced to 4 and 8 mm Hg respectively by repeat valvuloplasty. Balloon dilatation angioplasty was successful in dilating a severe stenosis at the lower limb of an atrial baffle (previous correction of complete transposition) and in dilating supravalvar stenosis of the pulmonary artery resulting from previous banding and debanding. Thus balloon pulmonary valvuloplasty, though still a new technique, appears to be the treatment of choice in patients with typical pulmonary stenosis and thin mobile valves. Patients with dysplastic valves may be less suitable candidates for the procedure. Balloon angioplasty is likely to have other applications, including the treatment of postoperative stenotic lesions.