Balloon valvuloplasty (BVP) of pulmonary stenosis (PST) was performed in 305 infants and children in 20 heart centres of the Federal Republic of Germany. 273 patients suffered from isolated PST. Their age ranged from 3 days to 18 years (mean = 5.85 +/- 4.82 years), their weight from 2.9 to 60 kg. The pressure gradient was measured invasively in the sedated or anaesthetized child, partly by CW Doppler. BVP was performed by mono- or trefoil catheters, mostly oversized. As a result, mean pressure gradient fell from 71.7 +/- 32 mmHg before to 31.8 +/- 25 mmHg immediately after BVP (P less than 0.0001). The gradient was reduced by less than 30% in 13% of the patients, by 30-49% in 23%, and by greater than or equal to 50% in 64%. Among 33 patients with a gradient reduction of less than 30%, nine were aged less than 1 year, nine had dysplastic valves, and nine had a short-term infundibular reaction and good late results. Gradient reduction was not improved with oversized balloons and was independent of the initial gradient. Follow-up for a mean 11.2 +/- 8 months showed a further slight improvement, probably due to regression of infundibular hypertrophy. In the whole group we observed infundibular reaction in 12%, serious complications with one late death in 4%. From the start, BVP proved to be a secure and effective tool for elimination of pulmonary stenosis.