Eight patients with mild to moderate valvular pulmonary stenosis underwent serial physiological studies before surgical intervention. Average pulmonary valve area at the initial study was 0.59 cm.2 and at the second study (average 7.8 years later) was 1.09 cm.2, resulting in an average increase of 0.49 cm.2 (p greater than 0.05). In normal subjects during early years the pulmonary valve area increases linearly with age and with increasing body surface area. Though patients with valvular pulmonary stenosis have smaller valve orifices, they also show an increase in valve size with increasing age and with increasing body growth. The greatest increase in valve area was observed in 4 patients (all under age 6) in whom body surface area increased more than 70 per cent.