The sulphidopeptide leukotrienes (C4, D4, and E4) are potent airway constrictors that have been detected in the airways of infants with pulmonary hypertension and viral infections. The present study was undertaken to test the hypothesis that leukotrienes in tracheal lavage fluid are elevated in bronchopulmonary dysplasia. Twenty-six intubated infants (10 with bronchopulmonary dysplasia, 9 with hyaline membrane disease, and 7 normal controls) had tracheal lavage leukotriene levels determined by radioimmunoassay. Lavage fluid cell counts (alveolar macrophages) and leukotriene levels were significantly increased in infants with severe bronchopulmonary dysplasia. The increased concentration of leukotrienes seen in the infants with bronchopulmonary dysplasia would suggest a possible role for these compounds in the pathophysiology of this disease.