Between July 1985 and March 1988, 22 adult patients with congenital pulmonary stenosis underwent balloon pulmonary valvuloplasty. There were 10 males and 12 females aged 16-45 (average 25 +/- 9.9) years. All patients had additional mild to severe infundibular stenosis; 16 were restudied 6-36 (mean 12.6) months later by repeat catheterization. Student's t-test was used for comparison of data. Right ventricular (RV) systolic pressure before dilatation was 84-196 (mean 129 +/- 32.3) mm Hg, and the peak pulmonary gradient (PPG) was 60-176 (mean 111 +/- 33.2) mm Hg immediately after dilatation. The RV systolic pressure dropped to 32-140 (mean 59.2 +/- 27) (P less than 0.001); and PPG dropped to 10-113 (mean 37.8 +/- 26.4) (P less than 0.001), and the infundibular gradient ranged from 8 to 113 (mean 35.1 +/- 25.8) mm Hg. The infundibular diameter, before dilatation, ranged from 2 to 15 (mean 9.5 +/- 4) mm Hg. At repeat catheterization, the RV systolic pressure dropped further to 33-66 (mean 42.8 +/- 9.7) mm Hg and the PPG was reduced to 0-48 (mean 18.4 +/- 10.9) mm Hg (P less than 0.001). The infundibular gradient regressed to 0-34 (mean 15 +/- 8.8) mm Hg (P less than 0.001). The infundibular diameter increased to 8-25 (mean 15.8 +/- 5.4) (P less than 0.001). It is concluded that moderate to severe infundibular stenosis, in adults, can regress after successful pulmonary valvuloplasty.