Glutathione (GSH) was measured using HPLC-electrochemical detection in bronchoalveolar lavage fluid from 28 neonates for up to 21 days after birth. GSH levels varied from 0.1-11.2 μmol l - 1 (with a geometric mean concentration of 1.3 μmol l - 1 ). GSH in epithelial lining fluid was estimated using the urea dilution method at 15.0 μmol l - 1 (range 0.5-196 μmol l - 1 ), which is significantly lower than observed in adult subjects. There was an L shaped relationship between GSH and the two markers of oxygen therapy, oxygen index and FiO 2 . The lowest GSH levels were associated with the group of infants with the most severe airways problems who required high oxygen.