A previous report has shown no difference between the clinical outcome of infants exposed to a high oxygen (O2) regimen and those exposed to a low O2 regimen for the treatment of respiratory distress syndrome (RDS). Mechanical ventilation was not used in either group. In the present study, pulmonary function tests were performed on 14 survivors receiving the low O2 regimen (low O2 group) and on nine receiving the high O2 regimen (high O2 group) ten years after their initial illness. Similar evidence of abnormalities of large airways was found in both groups of prematurely born children that was comparable with that previously reported for normal prematurely born children. There was evidence in the high O2 group similar to that reported for ventilated survivors with RDS exposed to a high concentration of O2. From these data, it was concluded that neonatal exposure to high O2 concentrations in the absence of mechanical ventilation is capable of causing long-term change in small airways.