To elucidate free radical-induced lung injury associated with open heart operations for congenital heart defects, we studied 23 such patients. Maximum plasma chemiluminescence level (a marker of peroxylipids) in patients with pulmonary hypertension (n = 8) was higher than in patients with cyanotic disease (n = 8) (1,115.4 +/- 189.9 versus 728.8 +/- 48.3 counts; p < 0.05). There was a significant correlation between the maximum chemiluminescence level and preoperative pulmonary to systemic arterial pressure ratio (r = 0.929; p < 0.05). To investigate the effect of allogeneic leukocytes, we compared pulmonary hypertensive patients without allogeneic leukocyte transfusion during operation (n = 7) with the group with pulmonary hypertension. Both maximum chemiluminescence level during bypass (712.4 +/- 24.9 versus 1,115.4 +/- 189.9 counts; p < 0.05) and percent decrease in pulmonary arterial pressure after bypass (44.7% +/- 6.2% versus 28.2% +/- 4.5%; p < 0.05) were significantly improved, suggesting that depletion of leukocytes decreased the lung injury induced by free radical reaction.